esm: phase two of new esm implementation

This PR updates the current `--experimental-modules` implementation based on the work of the modules team and reflects Phase 2 of our new modules plan. The largest differences from the current implementation include * `packge.type` which can be either `module` or `commonjs` - `type: "commonjs"`: - `.js` is parsed as commonjs - default for entry point without an extension is commonjs - `type: "module"`: - `.js` is parsed as esm - does not support loading JSON or Native Module by default - default for entry point without an extension is esm * `--entry-type=[mode]` - allows you set the type on entry point. * A new file extension `.cjs`. - this is specifically to support importing commonjs in the `module` mode. - this is only in the esm loader, the commonjs loader remains untouched, but the extension will work in the old loader if you use the full file path. * `--es-module-specifier-resolution=[type]` - options are `explicit` (default) and `node` - by default our loader will not allow for optional extensions in the import, the path for a module must include the extension if there is one - by default our loader will not allow for importing directories that have an index file - developers can use `--es-module-specifier-resolution=node` to enable the commonjs specifier resolution algorithm - This is not a “feature” but rather an implementation for experimentation. It is expected to change before the flag is removed * `--experimental-json-loader` - the only way to import json when `"type": "module"` - when enable all `import 'thing.json'` will go through the experimental loader independent of mode - based on https://github.com/whatwg/html/issues/4315 * You can use `package.main` to set an entry point for a module - the file extensions used in main will be resolved based on the `type` of the module Refs: https://github.com/nodejs/modules/blob/master/doc/plan-for-new-modules-implementation.md Refs: https://github.com/GeoffreyBooth/node-import-file-specifier-resolution-proposal Refs: https://github.com/nodejs/modules/pull/180 Refs: https://github.com/nodejs/ecmascript-modules/pull/6 Refs: https://github.com/nodejs/ecmascript-modules/pull/12 Refs: https://github.com/nodejs/ecmascript-modules/pull/28 Refs: https://github.com/nodejs/modules/issues/255 Refs: https://github.com/whatwg/html/issues/4315 Refs: https://github.com/w3c/webcomponents/issues/770 Co-authored-by: Myles Borins <MylesBorins@google.com> Co-authored-by: John-David Dalton <john.david.dalton@gmail.com> Co-authored-by: Evan Plaice <evanplaice@gmail.com> Co-authored-by: Geoffrey Booth <webmaster@geoffreybooth.com> Co-authored-by: Michaël Zasso <targos@protonmail.com> PR-URL: https://github.com/nodejs/node/pull/26745 Reviewed-By: Gus Caplan <me@gus.host> Reviewed-By: Guy Bedford <guybedford@gmail.com> Reviewed-By: Ben Coe <bencoe@gmail.com> Reviewed-By: James M Snell <jasnell@gmail.com> Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com> Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de> Reviewed-By: Сковорода Никита Андреевич <chalkerx@gmail.com>
2018-08-28 17:28:46 +02:00 · 2018-08-28 17:28:46 +02:00 · b1094dbe19
commit b1094dbe19
parent 39141426d4
124 changed files with 1834 additions and 494 deletions
--- a/.eslintrc.js
+++ b/.eslintrc.js
@ -38,6 +38,8 @@ module.exports = {
    {
      files: [
        'doc/api/esm.md',
        'test/es-module/test-esm-type-flag.js',
        'test/es-module/test-esm-type-flag-alias.js',
        '*.mjs',
        'test/es-module/test-esm-example-loader.js',
      ],
--- a/doc/api/cli.md
+++ b/doc/api/cli.md
@ -131,9 +131,43 @@ conjunction with native stack and other runtime environment data.
 added: v6.0.0
 -->
 ### `--entry-type=type`
 <!-- YAML
 added: REPLACEME
 -->
 Used with `--experimental-modules`, this configures Node.js to interpret the
 initial entry point as CommonJS or as an ES module.
 Valid values are `"commonjs"` and `"module"`. The default is to infer from
 the file extension and the `"type"` field in the nearest parent `package.json`.
 Works for executing a file as well as `--eval`, `--print`, `STDIN`.
 Enable FIPS-compliant crypto at startup. (Requires Node.js to be built with
 `./configure --openssl-fips`.)
 ### `--es-module-specifier-resolution=mode`
 <!-- YAML
 added: REPLACEME
 -->
 To be used in conjunction with `--experimental-modules`. Sets the resolution
 algorithm for resolving specifiers. Valid options are `explicit` and `node`.
 The default is `explicit`, which requires providing the full path to a
 module. The `node` mode will enable support for optional file extensions and
 the ability to import a directory that has an index file.
 Please see [customizing esm specifier resolution][] for example usage.
 ### `--experimental-json-modules`
 <!-- YAML
 added: REPLACEME
 -->
 Enable experimental JSON support for the ES Module loader.
 ### `--experimental-modules`
 <!-- YAML
 added: v8.5.0
@ -927,9 +961,10 @@ greater than `4` (its current default value). For more information, see the
 [REPL]: repl.html
 [ScriptCoverage]: https://chromedevtools.github.io/devtools-protocol/tot/Profiler#type-ScriptCoverage
 [V8 JavaScript code coverage]: https://v8project.blogspot.com/2017/12/javascript-code-coverage.html
 [customizing esm specifier resolution]: esm.html#esm_customizing_esm_specifier_resolution_algorithm
 [debugger]: debugger.html
 [debugging security implications]: https://nodejs.org/en/docs/guides/debugging-getting-started/#security-implications
 [emit_warning]: process.html#process_process_emitwarning_warning_type_code_ctor
-[experimental ECMAScript Module]: esm.html#esm_loader_hooks
+[experimental ECMAScript Module]: esm.html#esm_resolve_hook
 [libuv threadpool documentation]: http://docs.libuv.org/en/latest/threadpool.html
 [remote code execution]: https://www.owasp.org/index.php/Code_Injection
--- a/doc/api/errors.md
+++ b/doc/api/errors.md
@ -844,6 +844,18 @@ provided.
 Encoding provided to `TextDecoder()` API was not one of the
 [WHATWG Supported Encodings][].
 <a id="ERR_ENTRY_TYPE_MISMATCH"></a>
 #### ERR_ENTRY_TYPE_MISMATCH
 > Stability: 1 - Experimental
 The `--entry-type=commonjs` flag was used to attempt to execute an `.mjs` file
 or a `.js` file where the nearest parent `package.json` contains
 `"type": "module"`; or
 the `--entry-type=module` flag was used to attempt to execute a `.cjs` file or
 a `.js` file where the nearest parent `package.json` either lacks a `"type"`
 field or contains `"type": "commonjs"`.
 <a id="ERR_FALSY_VALUE_REJECTION"></a>
 ### ERR_FALSY_VALUE_REJECTION
@ -1267,6 +1279,11 @@ An invalid or unexpected value was passed in an options object.
 An invalid or unknown file encoding was passed.
 <a id="ERR_INVALID_PACKAGE_CONFIG"></a>
 ### ERR_INVALID_PACKAGE_CONFIG
 An invalid `package.json` file was found which failed parsing.
 <a id="ERR_INVALID_PERFORMANCE_MARK"></a>
 ### ERR_INVALID_PERFORMANCE_MARK
@ -1440,7 +1457,7 @@ strict compliance with the API specification (which in some cases may accept
 > Stability: 1 - Experimental
-An [ES6 module][] loader hook specified `format: 'dynamic'` but did not provide
+An [ES Module][] loader hook specified `format: 'dynamic'` but did not provide
 a `dynamicInstantiate` hook.
 <a id="ERR_MISSING_MESSAGE_PORT_IN_TRANSFER_LIST"></a>
@ -1449,13 +1466,6 @@ a `dynamicInstantiate` hook.
 A `MessagePort` was found in the object passed to a `postMessage()` call,
 but not provided in the `transferList` for that call.
 <a id="ERR_MISSING_MODULE"></a>
 ### ERR_MISSING_MODULE
 > Stability: 1 - Experimental
 An [ES6 module][] could not be resolved.
 <a id="ERR_MISSING_PLATFORM_FOR_WORKER"></a>
 ### ERR_MISSING_PLATFORM_FOR_WORKER
@ -1463,12 +1473,12 @@ The V8 platform used by this instance of Node.js does not support creating
 Workers. This is caused by lack of embedder support for Workers. In particular,
 this error will not occur with standard builds of Node.js.
-<a id="ERR_MODULE_RESOLUTION_LEGACY"></a>
+<a id="ERR_MODULE_NOT_FOUND"></a>
-### ERR_MODULE_RESOLUTION_LEGACY
+### ERR_MODULE_NOT_FOUND
 > Stability: 1 - Experimental
-A failure occurred resolving imports in an [ES6 module][].
+An [ES Module][] could not be resolved.
 <a id="ERR_MULTIPLE_CALLBACK"></a>
 ### ERR_MULTIPLE_CALLBACK
@ -1555,7 +1565,7 @@ A given value is out of the accepted range.
 > Stability: 1 - Experimental
-An attempt was made to `require()` an [ES6 module][].
+An attempt was made to `require()` an [ES Module][].
 <a id="ERR_SCRIPT_EXECUTION_INTERRUPTED"></a>
 ### ERR_SCRIPT_EXECUTION_INTERRUPTED
@ -2220,10 +2230,17 @@ A non-specific HTTP/2 error has occurred.
 Used in the `repl` in case the old history file is used and an error occurred
 while trying to read and parse it.
 <a id="ERR_INVALID_REPL_TYPE"></a>
 #### ERR_INVALID_REPL_TYPE
 > Stability: 1 - Experimental
 The `--entry-type=...` flag is not compatible with the Node.js REPL.
 <a id="ERR_MISSING_DYNAMIC_INSTANTIATE_HOOK"></a>
 #### ERR_MISSING_DYNAMIC_INSTANTIATE_HOOK
-Used when an [ES6 module][] loader hook specifies `format: 'dynamic'` but does
+Used when an [ES Module][] loader hook specifies `format: 'dynamic'` but does
 not provide a `dynamicInstantiate` hook.
 <a id="ERR_STREAM_HAS_STRINGDECODER"></a>
@ -2250,7 +2267,6 @@ size.
 This `Error` is thrown when a read is attempted on a TTY `WriteStream`,
 such as `process.stdout.on('data')`.
 [`'uncaughtException'`]: process.html#process_event_uncaughtexception
 [`--force-fips`]: cli.html#cli_force_fips
 [`Class: assert.AssertionError`]: assert.html#assert_class_assert_assertionerror
@ -2293,7 +2309,7 @@ such as `process.stdout.on('data')`.
 [`subprocess.kill()`]: child_process.html#child_process_subprocess_kill_signal
 [`subprocess.send()`]: child_process.html#child_process_subprocess_send_message_sendhandle_options_callback
 [`zlib`]: zlib.html
-[ES6 module]: esm.html
+[ES Module]: esm.html
 [ICU]: intl.html#intl_internationalization_support
 [Node.js Error Codes]: #nodejs-error-codes
 [V8's stack trace API]: https://github.com/v8/v8/wiki/Stack-Trace-API
--- a/doc/api/esm.md
+++ b/doc/api/esm.md
@ -5,39 +5,233 @@
 > Stability: 1 - Experimental
 ## Introduction
 <!--name=esm-->
-Node.js contains support for ES Modules based upon the
+ECMAScript modules are [the official standard format][] to package JavaScript
-[Node.js EP for ES Modules][].
+code for reuse. Modules are defined using a variety of [`import`][] and
 [`export`][] statements.
-Not all features of the EP are complete and will be landing as both VM support
+Node.js fully supports ECMAScript modules as they are currently specified and
-and implementation is ready. Error messages are still being polished.
+provides limited interoperability between them and the existing module format,
 [CommonJS][].
 Node.js contains support for ES Modules based upon the
 [Node.js EP for ES Modules][] and the [ECMAScript-modules implementation][].
 Expect major changes in the implementation including interoperability support,
 specifier resolution, and default behavior.
 ## Enabling
 <!-- type=misc -->
-The `--experimental-modules` flag can be used to enable features for loading
+The `--experimental-modules` flag can be used to enable support for
-ESM modules.
+ECMAScript modules (ES modules).
-Once this has been set, files ending with `.mjs` will be able to be loaded
+## Running Node.js with an ECMAScript Module
-as ES Modules.
+
 There are a few ways to start Node.js with an ES module as its input.
 ### Initial entry point with an <code>.mjs</code> extension
 A file ending with `.mjs` passed to Node.js as an initial entry point will be
 loaded as an ES module.
 ```sh
 node --experimental-modules my-app.mjs
 ```
-## Features
+### <code>--entry-type=module</code> flag
-<!-- type=misc -->
+Files ending with `.js` or `.mjs`, or lacking any extension,
 will be loaded as ES modules when the `--entry-type=module` flag is set.
-### Supported
+```sh
 node --experimental-modules --entry-type=module my-app.js
 ```
-Only the CLI argument for the main entry point to the program can be an entry
+For completeness there is also `--entry-type=commonjs`, for explicitly running
-point into an ESM graph. Dynamic import can also be used to create entry points
+a `.js` file as CommonJS. This is the default behavior if `--entry-type` is
-into ESM graphs at runtime.
+unspecified.
-#### import.meta
+The `--entry-type=module` flag can also be used to configure Node.js to treat
 as an ES module input sent in via `--eval` or `--print` (or `-e` or `-p`) or
 piped to Node.js via `STDIN`.
 ```sh
 node --experimental-modules --entry-type=module --eval \
  "import { sep } from 'path'; console.log(sep);"
 echo "import { sep } from 'path'; console.log(sep);" | \
  node --experimental-modules --entry-type=module
 ```
 ### <code>package.json</code> <code>"type"</code> field
 Files ending with `.js` or `.mjs`, or lacking any extension,
 will be loaded as ES modules when the nearest parent `package.json` file
 contains a top-level field `"type"` with a value of `"module"`.
 The nearest parent `package.json` is defined as the first `package.json` found
 when searching in the current folder, that folder’s parent, and so on up
 until the root of the volume is reached.
 <!-- eslint-skip -->
 ```js
 // package.json
 {
  "type": "module"
 }
 ```
 ```sh
 # In same folder as above package.json
 node --experimental-modules my-app.js # Runs as ES module
 ```
 If the nearest parent `package.json` lacks a `"type"` field, or contains
 `"type": "commonjs"`, extensionless and `.js` files are treated as CommonJS.
 If the volume root is reached and no `package.json` is found,
 Node.js defers to the default, a `package.json` with no `"type"`
 field.
 ## Package Scope and File Extensions
 A folder containing a `package.json` file, and all subfolders below that
 folder down until the next folder containing another `package.json`, is
 considered a _package scope_. The `"type"` field defines how `.js` and
 extensionless files should be treated within a particular `package.json` file’s
 package scope. Every package in a project’s `node_modules` folder contains its
 own `package.json` file, so each project’s dependencies have their own package
 scopes. A `package.json` lacking a `"type"` field is treated as if it contained
 `"type": "commonjs"`.
 The package scope applies not only to initial entry points (`node
 --experimental-modules my-app.js`) but also to files referenced by `import`
 statements and `import()` expressions.
 ```js
 // my-app.js, in an ES module package scope because there is a package.json
 // file in the same folder with "type": "module".
 import './startup/init.js';
 // Loaded as ES module since ./startup contains no package.json file,
 // and therefore inherits the ES module package scope from one level up.
 import 'commonjs-package';
 // Loaded as CommonJS since ./node_modules/commonjs-package/package.json
 // lacks a "type" field or contains "type": "commonjs".
 import './node_modules/commonjs-package/index.js';
 // Loaded as CommonJS since ./node_modules/commonjs-package/package.json
 // lacks a "type" field or contains "type": "commonjs".
 ```
 Files ending with `.mjs` are always loaded as ES modules regardless of package
 scope.
 Files ending with `.cjs` are always loaded as CommonJS regardless of package
 scope.
 ```js
 import './legacy-file.cjs';
 // Loaded as CommonJS since .cjs is always loaded as CommonJS.
 import 'commonjs-package/src/index.mjs';
 // Loaded as ES module since .mjs is always loaded as ES module.
 ```
 The `.mjs` and `.cjs` extensions may be used to mix types within the same
 package scope:
 - Within a `"type": "module"` package scope, Node.js can be instructed to
  interpret a particular file as CommonJS by naming it with a `.cjs` extension
  (since both `.js` and `.mjs` files are treated as ES modules within a
  `"module"` package scope).
 - Within a `"type": "commonjs"` package scope, Node.js can be instructed to
  interpret a particular file as an ES module by naming it with an `.mjs`
  extension (since both `.js` and `.cjs` files are treated as CommonJS within a
  `"commonjs"` package scope).
 ## Package Entry Points
 The `package.json` `"main"` field defines the entry point for a package,
 whether the package is included into CommonJS via `require` or into an ES
 module via `import`.
 <!-- eslint-skip -->
 ```js
 // ./node_modules/es-module-package/package.json
 {
  "type": "module",
  "main": "./src/index.js"
 }
 ```
 ```js
 // ./my-app.mjs
 import { something } from 'es-module-package';
 // Loads from ./node_modules/es-module-package/src/index.js
 ```
 An attempt to `require` the above `es-module-package` would attempt to load
 `./node_modules/es-module-package/src/index.js` as CommonJS, which would throw
 an error as Node.js would not be able to parse the `export` statement in
 CommonJS.
 As with `import` statements, for ES module usage the value of `"main"` must be
 a full path including extension: `"./index.mjs"`, not `"./index"`.
 If the `package.json` `"type"` field is omitted, a `.js` file in `"main"` will
 be interpreted as CommonJS.
 > Currently a package can define _either_ a CommonJS entry point **or** an ES
 > module entry point; there is no way to specify separate entry points for
 > CommonJS and ES module usage. This means that a package entry point can be
 > included via `require` or via `import` but not both.
 >
 > Such a limitation makes it difficult for packages to support both new versions
 > of Node.js that understand ES modules and older versions of Node.js that
 > understand only CommonJS. There is work ongoing to remove this limitation, and
 > it will very likely entail changes to the behavior of `"main"` as defined
 > here.
 ## <code>import</code> Specifiers
 ### Terminology
 The _specifier_ of an `import` statement is the string after the `from` keyword,
 e.g. `'path'` in `import { sep } from 'path'`. Specifiers are also used in
 `export from` statements, and as the argument to an `import()` expression.
 There are four types of specifiers:
 - _Bare specifiers_ like `'some-package'`. They refer to an entry point of a
  package by the package name.
 - _Deep import specifiers_ like `'some-package/lib/shuffle.mjs'`. They refer to
  a path within a package prefixed by the package name.
 - _Relative specifiers_ like `'./startup.js'` or `'../config.mjs'`. They refer
  to a path relative to the location of the importing file.
 - _Absolute specifiers_ like `'file:///opt/nodejs/config.js'`. They refer
  directly and explicitly to a full path.
 Bare specifiers, and the bare specifier portion of deep import specifiers, are
 strings; but everything else in a specifier is a URL.
 Only `file://` URLs are supported. A specifier like
 `'https://example.com/app.js'` may be supported by browsers but it is not
 supported in Node.js.
 Specifiers may not begin with `/` or `//`. These are reserved for potential
 future use. The root of the current volume may be referenced via `file:///`.
 ## import.meta
 * {Object}
@ -46,63 +240,128 @@ property:
 * `url` {string} The absolute `file:` URL of the module.
-### Unsupported
+## Differences Between ES Modules and CommonJS
-| Feature | Reason |
+### Mandatory file extensions
 | --- | --- |
 | `require('./foo.mjs')` | ES Modules have differing resolution and timing, use dynamic import |
-## Notable differences between `import` and `require`
+A file extension must be provided when using the `import` keyword. Directory
 indexes (e.g. `'./startup/index.js'`) must also be fully specified.
-### No NODE_PATH
+This behavior matches how `import` behaves in browser environments, assuming a
 typically configured server.
 ### No <code>NODE_PATH</code>
 `NODE_PATH` is not part of resolving `import` specifiers. Please use symlinks
 if this behavior is desired.
-### No `require.extensions`
+### No <code>require</code>, <code>exports</code>, <code>module.exports</code>, <code>\_\_filename</code>, <code>\_\_dirname</code>
 These CommonJS variables are not available in ES modules.
 `require` can be imported into an ES module using
 [`module.createRequireFromPath()`][].
 An equivalent for `__filename` and `__dirname` is [`import.meta.url`][].
 ### No <code>require.extensions</code>
 `require.extensions` is not used by `import`. The expectation is that loader
 hooks can provide this workflow in the future.
-### No `require.cache`
+### No <code>require.cache</code>
 `require.cache` is not used by `import`. It has a separate cache.
-### URL based paths
+### URL-based paths
-ESM are resolved and cached based upon [URL](https://url.spec.whatwg.org/)
+ES modules are resolved and cached based upon
-semantics. This means that files containing special characters such as `#` and
+[URL](https://url.spec.whatwg.org/) semantics. This means that files containing
-`?` need to be escaped.
+special characters such as `#` and `?` need to be escaped.
 Modules will be loaded multiple times if the `import` specifier used to resolve
 them have a different query or fragment.
 ```js
-import './foo?query=1'; // loads ./foo with query of "?query=1"
+import './foo.mjs?query=1'; // loads ./foo.mjs with query of "?query=1"
-import './foo?query=2'; // loads ./foo with query of "?query=2"
+import './foo.mjs?query=2'; // loads ./foo.mjs with query of "?query=2"
 ```
 For now, only modules using the `file:` protocol can be loaded.
-## Interop with existing modules
+## Interoperability with CommonJS
-All CommonJS, JSON, and C++ modules can be used with `import`.
+### <code>require</code>
-Modules loaded this way will only be loaded once, even if their query
+`require` always treats the files it references as CommonJS. This applies
-or fragment string differs between `import` statements.
+whether `require` is used the traditional way within a CommonJS environment, or
 in an ES module environment using [`module.createRequireFromPath()`][].
-When loaded via `import` these modules will provide a single `default` export
+To include an ES module into CommonJS, use [`import()`][].
-representing the value of `module.exports` at the time they finished evaluating.
+
 ### <code>import</code> statements
 An `import` statement can reference either ES module or CommonJS JavaScript.
 Other file types such as JSON and Native modules are not supported. For those,
 use [`module.createRequireFromPath()`][].
 `import` statements are permitted only in ES modules. For similar functionality
 in CommonJS, see [`import()`][].
 The _specifier_ of an `import` statement (the string after the `from` keyword)
 can either be an URL-style relative path like `'./file.mjs'` or a package name
 like `'fs'`.
 Like in CommonJS, files within packages can be accessed by appending a path to
 the package name.
 ```js
-// foo.js
+import { sin, cos } from 'geometry/trigonometry-functions.mjs';
 module.exports = { one: 1 };
 // bar.mjs
 import foo from './foo.js';
 foo.one === 1; // true
 ```
 > Currently only the “default export” is supported for CommonJS files or
 > packages:
 >
 > <!-- eslint-disable no-duplicate-imports -->
 > ```js
 > import packageMain from 'commonjs-package'; // Works
 >
 > import { method } from 'commonjs-package'; // Errors
 > ```
 >
 > There are ongoing efforts to make the latter code possible.
 ### <code>import()</code> expressions
 Dynamic `import()` is supported in both CommonJS and ES modules. It can be used
 to include ES module files from CommonJS code.
 ```js
 (async () => {
  await import('./my-app.mjs');
 })();
 ```
 ## CommonJS, JSON, and Native Modules
 CommonJS, JSON, and Native modules can be used with [`module.createRequireFromPath()`][].
 ```js
 // cjs.js
 module.exports = 'cjs';
 // esm.mjs
 import { createRequireFromPath as createRequire } from 'module';
 import { fileURLToPath as fromURL } from 'url';
 const require = createRequire(fromURL(import.meta.url));
 const cjs = require('./cjs');
 cjs === 'cjs'; // true
 ```
 ## Builtin modules
 Builtin modules will provide named exports of their public API, as well as a
 default export which can be used for, among other things, modifying the named
 exports. Named exports of builtin modules are updated when the corresponding
@ -132,7 +391,41 @@ fs.readFileSync = () => Buffer.from('Hello, ESM');
 fs.readFileSync === readFileSync;
 ```
-## Loader hooks
+## Experimental JSON Modules
 **Note: This API is still being designed and is subject to change.**
 Currently importing JSON modules are only supported in the `commonjs` mode
 and are loaded using the CJS loader. [WHATWG JSON modules][] are currently
 being standardized, and are experimentally supported by including the
 additional flag `--experimental-json-modules` when running Node.js.
 When the `--experimental-json-modules` flag is included both the
 `commonjs` and `module` mode will use the new experimental JSON
 loader. The imported JSON only exposes a `default`, there is no
 support for named exports. A cache entry is created in the CommonJS
 cache, to avoid duplication. The same object will be returned in
 CommonJS if the JSON module has already been imported from the
 same path.
 Assuming an `index.js` with
 <!-- eslint-skip -->
 ```js
 import packageConfig from './package.json';
 ```
 The `--experimental-json-modules` flag is needed for the module
 to work.
 ```bash
 node --experimental-modules --entry-type=module index.js # fails
 node --experimental-modules --entry-type=module --experimental-json-modules index.js # works
 ```
 ## Experimental Loader hooks
 **Note: This API is currently being redesigned and will still change.**
 <!-- type=misc -->
@ -173,11 +466,10 @@ module. This can be one of the following:
 | `format` | Description |
 | --- | --- |
-| `'esm'` | Load a standard JavaScript module |
+| `'module'` | Load a standard JavaScript module |
-| `'cjs'` | Load a node-style CommonJS module |
+| `'commonjs'` | Load a Node.js CommonJS module |
-| `'builtin'` | Load a node builtin CommonJS module |
+| `'builtin'` | Load a Node.js builtin module |
 | `'json'` | Load a JSON file |
 | `'addon'` | Load a [C++ Addon][addons] |
 | `'dynamic'` | Use a [dynamic instantiate hook][] |
 For example, a dummy loader to load JavaScript restricted to browser resolution
@ -253,6 +545,184 @@ With the list of module exports provided upfront, the `execute` function will
 then be called at the exact point of module evaluation order for that module
 in the import tree.
 ## Resolution Algorithm
 ### Features
 The resolver has the following properties:
 * FileURL-based resolution as is used by ES modules
 * Support for builtin module loading
 * Relative and absolute URL resolution
 * No default extensions
 * No folder mains
 * Bare specifier package resolution lookup through node_modules
 ### Resolver Algorithm
 The algorithm to load an ES module specifier is given through the
 **ESM_RESOLVE** method below. It returns the resolved URL for a
 module specifier relative to a parentURL, in addition to the unique module
 format for that resolved URL given by the **ESM_FORMAT** routine.
 The _"module"_ format is returned for an ECMAScript Module, while the
 _"commonjs"_ format is used to indicate loading through the legacy
 CommonJS loader. Additional formats such as _"wasm"_ or _"addon"_ can be
 extended in future updates.
 In the following algorithms, all subroutine errors are propagated as errors
 of these top-level routines.
 _isMain_ is **true** when resolving the Node.js application entry point.
 When using the `--entry-type` flag, it overrides the ESM_FORMAT result while
 providing errors in the case of explicit conflicts.
 <details>
 <summary>Resolver algorithm specification</summary>
 **ESM_RESOLVE(_specifier_, _parentURL_, _isMain_)**
 > 1. Let _resolvedURL_ be **undefined**.
 > 1. If _specifier_ is a valid URL, then
 >    1. Set _resolvedURL_ to the result of parsing and reserializing
 >       _specifier_ as a URL.
 > 1. Otherwise, if _specifier_ starts with _"/"_, then
 >    1. Throw an _Invalid Specifier_ error.
 > 1. Otherwise, if _specifier_ starts with _"./"_ or _"../"_, then
 >    1. Set _resolvedURL_ to the URL resolution of _specifier_ relative to
 >       _parentURL_.
 > 1. Otherwise,
 >    1. Note: _specifier_ is now a bare specifier.
 >    1. Set _resolvedURL_ the result of
 >       **PACKAGE_RESOLVE**(_specifier_, _parentURL_).
 > 1. If the file at _resolvedURL_ does not exist, then
 >    1. Throw a _Module Not Found_ error.
 > 1. Set _resolvedURL_ to the real path of _resolvedURL_.
 > 1. Let _format_ be the result of **ESM_FORMAT**(_resolvedURL_, _isMain_).
 > 1. Load _resolvedURL_ as module format, _format_.
 PACKAGE_RESOLVE(_packageSpecifier_, _parentURL_)
 > 1. Let _packageName_ be *undefined*.
 > 1. Let _packageSubpath_ be *undefined*.
 > 1. If _packageSpecifier_ is an empty string, then
 >    1. Throw an _Invalid Specifier_ error.
 > 1. If _packageSpecifier_ does not start with _"@"_, then
 >    1. Set _packageName_ to the substring of _packageSpecifier_ until the
 >       first _"/"_ separator or the end of the string.
 > 1. Otherwise,
 >    1. If _packageSpecifier_ does not contain a _"/"_ separator, then
 >       1. Throw an _Invalid Specifier_ error.
 >    1. Set _packageName_ to the substring of _packageSpecifier_
 >       until the second _"/"_ separator or the end of the string.
 > 1. Let _packageSubpath_ be the substring of _packageSpecifier_ from the
 >    position at the length of _packageName_ plus one, if any.
 > 1. Assert: _packageName_ is a valid package name or scoped package name.
 > 1. Assert: _packageSubpath_ is either empty, or a path without a leading
 >    separator.
 > 1. If _packageSubpath_ contains any _"."_ or _".."_ segments or percent
 >    encoded strings for _"/"_ or _"\\"_ then,
 >    1. Throw an _Invalid Specifier_ error.
 > 1. If _packageSubpath_ is empty and _packageName_ is a Node.js builtin
 >    module, then
 >    1. Return the string _"node:"_ concatenated with _packageSpecifier_.
 > 1. While _parentURL_ is not the file system root,
 >    1. Let _packageURL_ be the URL resolution of "node_modules/"
 >       concatenated with _packageSpecifier_, relative to _parentURL_.
 >    1. Set _parentURL_ to the parent folder URL of _parentURL_.
 >    1. If the folder at _packageURL_ does not exist, then
 >       1. Set _parentURL_ to the parent URL path of _parentURL_.
 >       1. Continue the next loop iteration.
 >    1. Let _pjson_ be the result of **READ_PACKAGE_JSON**(_packageURL_).
 >    1. If _packageSubpath_ is empty, then
 >       1. Return the result of **PACKAGE_MAIN_RESOLVE**(_packageURL_,
 >          _pjson_).
 >    1. Otherwise,
 >       1. Return the URL resolution of _packageSubpath_ in _packageURL_.
 > 1. Throw a _Module Not Found_ error.
 PACKAGE_MAIN_RESOLVE(_packageURL_, _pjson_)
 > 1. If _pjson_ is **null**, then
 >    1. Throw a _Module Not Found_ error.
 > 1. If _pjson.main_ is a String, then
 >    1. Let _resolvedMain_ be the concatenation of _packageURL_, "/", and
 >       _pjson.main_.
 >    1. If the file at _resolvedMain_ exists, then
 >       1. Return _resolvedMain_.
 > 1. If _pjson.type_ is equal to _"module"_, then
 >    1. Throw a _Module Not Found_ error.
 > 1. Let _legacyMainURL_ be the result applying the legacy
 >    **LOAD_AS_DIRECTORY** CommonJS resolver to _packageURL_, throwing a
 >    _Module Not Found_ error for no resolution.
 > 1. If _legacyMainURL_ does not end in _".js"_ then,
 >    1. Throw an _Unsupported File Extension_ error.
 > 1. Return _legacyMainURL_.
 **ESM_FORMAT(_url_, _isMain_)**
 > 1. Assert: _url_ corresponds to an existing file.
 > 1. Let _pjson_ be the result of **READ_PACKAGE_SCOPE**(_url_).
 > 1. If _url_ ends in _".mjs"_, then
 >    1. Return _"module"_.
 > 1. If _url_ ends in _".cjs"_, then
 >    1. Return _"commonjs"_.
 > 1. If _pjson?.type_ exists and is _"module"_, then
 >    1. If _isMain_ is **true** or _url_ ends in _".js"_, then
 >       1. Return _"module"_.
 >    1. Throw an _Unsupported File Extension_ error.
 > 1. Otherwise,
 >    1. If _isMain_ is **true** or _url_ ends in _".js"_, _".json"_ or
 >       _".node"_, then
 >       1. Return _"commonjs"_.
 >    1. Throw an _Unsupported File Extension_ error.
 READ_PACKAGE_SCOPE(_url_)
 > 1. Let _scopeURL_ be _url_.
 > 1. While _scopeURL_ is not the file system root,
 >    1. Let _pjson_ be the result of **READ_PACKAGE_JSON**(_scopeURL_).
 >    1. If _pjson_ is not **null**, then
 >       1. Return _pjson_.
 >    1. Set _scopeURL_ to the parent URL of _scopeURL_.
 > 1. Return **null**.
 READ_PACKAGE_JSON(_packageURL_)
 > 1. Let _pjsonURL_ be the resolution of _"package.json"_ within _packageURL_.
 > 1. If the file at _pjsonURL_ does not exist, then
 >    1. Return **null**.
 > 1. If the file at _packageURL_ does not parse as valid JSON, then
 >    1. Throw an _Invalid Package Configuration_ error.
 > 1. Return the parsed JSON source of the file at _pjsonURL_.
 </details>
 ### Customizing ESM specifier resolution algorithm
 The current specifier resolution does not support all default behavior of
 the CommonJS loader. One of the behavior differences is automatic resolution
 of file extensions and the ability to import directories that have an index
 file.
 The `--es-module-specifier-resolution=[mode]` flag can be used to customize
 the extension resolution algorithm. The default mode is `explicit`, which
 requires the full path to a module be provided to the loader. To enable the
 automatic extension resolution and importing from directories that include an
 index file use the `node` mode.
 ```bash
 $ node --experimental-modules index.mjs
 success!
 $ node --experimental-modules index #Failure!
 Error: Cannot find module
 $ node --experimental-modules --es-module-specifier-resolution=node index
 success!
 ```
 [`export`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/export
 [`import`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/import
 [`import()`]: #esm_import-expressions
 [`import.meta.url`]: #esm_import_meta
 [`module.createRequireFromPath()`]: modules.html#modules_module_createrequirefrompath_filename
 [CommonJS]: modules.html
 [ECMAScript-modules implementation]: https://github.com/nodejs/modules/blob/master/doc/plan-for-new-modules-implementation.md
 [Node.js EP for ES Modules]: https://github.com/nodejs/node-eps/blob/master/002-es-modules.md
-[addons]: addons.html
+[WHATWG JSON modules]: https://github.com/whatwg/html/issues/4315
 [dynamic instantiate hook]: #esm_dynamic_instantiate_hook
 [the official standard format]: https://tc39.github.io/ecma262/#sec-modules
--- a/doc/node.1
+++ b/doc/node.1
@ -119,6 +119,15 @@ Enable FIPS-compliant crypto at startup.
 Requires Node.js to be built with
 .Sy ./configure --openssl-fips .
 .
 .It Fl -entry-type Ns = Ns Ar type
 Set the top-level module resolution type.
 .
 .It Fl -es-module-specifier-resolution
 Select extension resolution algorithm for ES Modules; either 'explicit' (default) or 'node'
 .
 .It Fl -experimental-json-modules
 Enable experimental JSON interop support for the ES Module loader.
 .
 .It Fl -experimental-modules
 Enable experimental ES module support and caching modules.
 .
--- a/lib/internal/bootstrap/pre_execution.js
+++ b/lib/internal/bootstrap/pre_execution.js
@ -323,6 +323,10 @@ function initializeESMLoader() {
    const userLoader = getOptionValue('--loader');
    // If --loader is specified, create a loader with user hooks. Otherwise
    // create the default loader.
    if (userLoader) {
      const { emitExperimentalWarning } = require('internal/util');
      emitExperimentalWarning('--loader');
    }
    esm.initializeLoader(process.cwd(), userLoader);
  }
 }
--- a/lib/internal/errors.js
+++ b/lib/internal/errors.js
@ -678,6 +678,24 @@ E('ERR_ENCODING_INVALID_ENCODED_DATA', function(encoding, ret) {
 }, TypeError);
 E('ERR_ENCODING_NOT_SUPPORTED', 'The "%s" encoding is not supported',
  RangeError);
 E('ERR_ENTRY_TYPE_MISMATCH', (filename, ext, typeFlag, conflict) => {
  const typeString =
    typeFlag === 'module' ? '--entry-type=module' : '--entry-type=commonjs';
  // --entry-type mismatches file extension
  if (conflict === 'extension') {
    return `Extension ${ext} is not supported for ` +
      `${typeString} loading ${filename}`;
  }
  assert(
    conflict === 'scope',
    '"conflict" value unknown. Set this argument to "extension" or "scope"'
  );
  // --entry-type mismatches package.json "type"
  return `Cannot use ${typeString} because nearest parent package.json ` +
    ((typeFlag === 'module') ?
      'includes "type": "commonjs"' : 'includes "type": "module",') +
    ` which controls the type to use for ${filename}`;
 }, TypeError);
 E('ERR_FALSY_VALUE_REJECTION', function(reason) {
  this.reason = reason;
  return 'Promise was rejected with falsy value';
@ -864,6 +882,8 @@ E('ERR_INVALID_OPT_VALUE', (name, value) =>
  RangeError);
 E('ERR_INVALID_OPT_VALUE_ENCODING',
  'The value "%s" is invalid for option "encoding"', TypeError);
 E('ERR_INVALID_PACKAGE_CONFIG',
  'Invalid package config in \'%s\' imported from %s', Error);
 E('ERR_INVALID_PERFORMANCE_MARK',
  'The "%s" performance mark has not been set', Error);
 E('ERR_INVALID_PROTOCOL',
@ -958,11 +978,6 @@ E('ERR_MISSING_ARGS',
 E('ERR_MISSING_DYNAMIC_INSTANTIATE_HOOK',
  'The ES Module loader may not return a format of \'dynamic\' when no ' +
  'dynamicInstantiate function was provided', Error);
 E('ERR_MISSING_MODULE', 'Cannot find module %s', Error);
 E('ERR_MODULE_RESOLUTION_LEGACY',
  '%s not found by import in %s.' +
    ' Legacy behavior in require() would have found it at %s',
  Error);
 E('ERR_MULTIPLE_CALLBACK', 'Callback called multiple times', Error);
 E('ERR_NAPI_CONS_FUNCTION', 'Constructor must be a function', TypeError);
 E('ERR_NAPI_INVALID_DATAVIEW_ARGS',
@ -1067,9 +1082,7 @@ E('ERR_UNHANDLED_ERROR',
 E('ERR_UNKNOWN_BUILTIN_MODULE', 'No such built-in module: %s', Error);
 E('ERR_UNKNOWN_CREDENTIAL', '%s identifier does not exist: %s', Error);
 E('ERR_UNKNOWN_ENCODING', 'Unknown encoding: %s', TypeError);
-
+E('ERR_UNKNOWN_FILE_EXTENSION', 'Unknown file extension: %s', TypeError);
 // This should probably be a `TypeError`.
 E('ERR_UNKNOWN_FILE_EXTENSION', 'Unknown file extension: %s', Error);
 E('ERR_UNKNOWN_MODULE_FORMAT', 'Unknown module format: %s', RangeError);
 E('ERR_UNKNOWN_SIGNAL', 'Unknown signal: %s', TypeError);
--- a/lib/internal/main/check_syntax.js
+++ b/lib/internal/main/check_syntax.js
@ -11,12 +11,18 @@ const {
  readStdin
 } = require('internal/process/execution');
-const CJSModule = require('internal/modules/cjs/loader');
+const { pathToFileURL } = require('url');
 const vm = require('vm');
 const {
  stripShebang, stripBOM
 } = require('internal/modules/cjs/helpers');
 let CJSModule;
 function CJSModuleInit() {
  if (!CJSModule)
    CJSModule = require('internal/modules/cjs/loader');
 }
 if (process.argv[1] && process.argv[1] !== '-') {
  // Expand process.argv[1] into a full path.
@ -25,7 +31,7 @@ if (process.argv[1] && process.argv[1] !== '-') {
  // TODO(joyeecheung): not every one of these are necessary
  prepareMainThreadExecution();
-
+  CJSModuleInit();
  // Read the source.
  const filename = CJSModule._resolveFilename(process.argv[1]);
@ -34,20 +40,40 @@ if (process.argv[1] && process.argv[1] !== '-') {
  markBootstrapComplete();
-  checkScriptSyntax(source, filename);
+  checkSyntax(source, filename);
 } else {
  // TODO(joyeecheung): not every one of these are necessary
  prepareMainThreadExecution();
  CJSModuleInit();
  markBootstrapComplete();
  readStdin((code) => {
-    checkScriptSyntax(code, '[stdin]');
+    checkSyntax(code, '[stdin]');
  });
 }
-function checkScriptSyntax(source, filename) {
+function checkSyntax(source, filename) {
  // Remove Shebang.
  source = stripShebang(source);
  const { getOptionValue } = require('internal/options');
  const experimentalModules = getOptionValue('--experimental-modules');
  if (experimentalModules) {
    let isModule = false;
    if (filename === '[stdin]' || filename === '[eval]') {
      isModule = getOptionValue('--entry-type') === 'module';
    } else {
      const resolve = require('internal/modules/esm/default_resolve');
      const { format } = resolve(pathToFileURL(filename).toString());
      isModule = format === 'module';
    }
    if (isModule) {
      const { ModuleWrap } = internalBinding('module_wrap');
      new ModuleWrap(source, filename);
      return;
    }
  }
  // Remove BOM.
  source = stripBOM(source);
  // Wrap it.
--- a/lib/internal/main/eval_stdin.js
+++ b/lib/internal/main/eval_stdin.js
@ -7,6 +7,7 @@ const {
 } = require('internal/bootstrap/pre_execution');
 const {
  evalModule,
  evalScript,
  readStdin
 } = require('internal/process/execution');
@ -16,5 +17,8 @@ markBootstrapComplete();
 readStdin((code) => {
  process._eval = code;
-  evalScript('[stdin]', process._eval, process._breakFirstLine);
+  if (require('internal/options').getOptionValue('--entry-type') === 'module')
    evalModule(process._eval);
  else
    evalScript('[stdin]', process._eval, process._breakFirstLine);
 });
--- a/lib/internal/main/eval_string.js
+++ b/lib/internal/main/eval_string.js
@ -6,11 +6,15 @@
 const {
  prepareMainThreadExecution
 } = require('internal/bootstrap/pre_execution');
-const { evalScript } = require('internal/process/execution');
+const { evalModule, evalScript } = require('internal/process/execution');
 const { addBuiltinLibsToObject } = require('internal/modules/cjs/helpers');
-const source = require('internal/options').getOptionValue('--eval');
+const { getOptionValue } = require('internal/options');
 const source = getOptionValue('--eval');
 prepareMainThreadExecution();
 addBuiltinLibsToObject(global);
 markBootstrapComplete();
-evalScript('[eval]', source, process._breakFirstLine);
+if (getOptionValue('--entry-type') === 'module')
  evalModule(source);
 else
  evalScript('[eval]', source, process._breakFirstLine);
--- a/lib/internal/main/repl.js
+++ b/lib/internal/main/repl.js
@ -13,6 +13,12 @@ const {
 prepareMainThreadExecution();
 // --entry-type flag not supported in REPL
 if (require('internal/options').getOptionValue('--entry-type')) {
  console.error('Cannot specify --entry-type for REPL');
  process.exit(1);
 }
 const cliRepl = require('internal/repl');
 cliRepl.createInternalRepl(process.env, (err, repl) => {
  if (err) {
--- a/lib/internal/modules/cjs/loader.js
+++ b/lib/internal/modules/cjs/loader.js
@ -896,9 +896,11 @@ Module.runMain = function() {
    .catch((e) => {
      internalBinding('task_queue').triggerFatalException(e);
    });
-  } else {
+    // Handle any nextTicks added in the first tick of the program
-    Module._load(process.argv[1], null, true);
+    process._tickCallback();
    return;
  }
  Module._load(process.argv[1], null, true);
  // Handle any nextTicks added in the first tick of the program
  process._tickCallback();
 };
--- a/lib/internal/modules/esm/default_resolve.js
+++ b/lib/internal/modules/esm/default_resolve.js
@ -1,57 +1,54 @@
 'use strict';
 const { URL } = require('url');
 const CJSmodule = require('internal/modules/cjs/loader');
 const internalFS = require('internal/fs/utils');
 const { NativeModule } = require('internal/bootstrap/loaders');
 const { extname } = require('path');
 const { realpathSync } = require('fs');
 const { getOptionValue } = require('internal/options');
 const preserveSymlinks = getOptionValue('--preserve-symlinks');
 const preserveSymlinksMain = getOptionValue('--preserve-symlinks-main');
-const {
+const experimentalJsonModules = getOptionValue('--experimental-json-modules');
-  ERR_MISSING_MODULE,
+const typeFlag = getOptionValue('--entry-type');
-  ERR_MODULE_RESOLUTION_LEGACY,
+
-  ERR_UNKNOWN_FILE_EXTENSION
+const { resolve: moduleWrapResolve,
-} = require('internal/errors').codes;
+        getPackageType } = internalBinding('module_wrap');
 const { resolve: moduleWrapResolve } = internalBinding('module_wrap');
 const StringStartsWith = Function.call.bind(String.prototype.startsWith);
 const { pathToFileURL, fileURLToPath } = require('internal/url');
 const { ERR_ENTRY_TYPE_MISMATCH,
        ERR_UNKNOWN_FILE_EXTENSION } = require('internal/errors').codes;
 const realpathCache = new Map();
-function search(target, base) {
+// const TYPE_NONE = 0;
-  if (base === undefined) {
+const TYPE_COMMONJS = 1;
-    // We cannot search without a base.
+const TYPE_MODULE = 2;
    throw new ERR_MISSING_MODULE(target);
  }
  try {
    return moduleWrapResolve(target, base);
  } catch (e) {
    e.stack; // cause V8 to generate stack before rethrow
    let error = e;
    try {
      const questionedBase = new URL(base);
      const tmpMod = new CJSmodule(questionedBase.pathname, null);
      tmpMod.paths = CJSmodule._nodeModulePaths(
        new URL('./', questionedBase).pathname);
      const found = CJSmodule._resolveFilename(target, tmpMod);
      error = new ERR_MODULE_RESOLUTION_LEGACY(target, base, found);
    } catch {
      // ignore
    }
    throw error;
  }
 }
 const extensionFormatMap = {
  '__proto__': null,
-  '.mjs': 'esm',
+  '.cjs': 'commonjs',
-  '.json': 'json',
+  '.js': 'module',
-  '.node': 'addon',
+  '.mjs': 'module'
  '.js': 'cjs'
 };
 const legacyExtensionFormatMap = {
  '__proto__': null,
  '.cjs': 'commonjs',
  '.js': 'commonjs',
  '.json': 'commonjs',
  '.mjs': 'module',
  '.node': 'commonjs'
 };
 if (experimentalJsonModules) {
  // This is a total hack
  Object.assign(extensionFormatMap, {
    '.json': 'json'
  });
  Object.assign(legacyExtensionFormatMap, {
    '.json': 'json'
  });
 }
 function resolve(specifier, parentURL) {
  if (NativeModule.canBeRequiredByUsers(specifier)) {
    return {
@ -60,21 +57,11 @@ function resolve(specifier, parentURL) {
    };
  }
  let url;
  try {
    url = search(specifier,
                 parentURL || pathToFileURL(`${process.cwd()}/`).href);
  } catch (e) {
    if (typeof e.message === 'string' &&
        StringStartsWith(e.message, 'Cannot find module')) {
      e.code = 'MODULE_NOT_FOUND';
      // TODO: also add e.requireStack to match behavior with CJS
      // MODULE_NOT_FOUND.
    }
    throw e;
  }
  const isMain = parentURL === undefined;
  if (isMain)
    parentURL = pathToFileURL(`${process.cwd()}/`).href;
  let url = moduleWrapResolve(specifier, parentURL);
  if (isMain ? !preserveSymlinksMain : !preserveSymlinks) {
    const real = realpathSync(fileURLToPath(url), {
@ -86,19 +73,40 @@ function resolve(specifier, parentURL) {
    url.hash = old.hash;
  }
  const type = getPackageType(url.href);
  const ext = extname(url.pathname);
  const extMap =
      type !== TYPE_MODULE ? legacyExtensionFormatMap : extensionFormatMap;
  let format = extMap[ext];
-  let format = extensionFormatMap[ext];
+  if (isMain && typeFlag) {
-  if (!format) {
+    // Conflict between explicit extension (.mjs, .cjs) and --entry-type
-    if (isMain)
+    if (ext === '.cjs' && typeFlag === 'module' ||
-      format = 'cjs';
+        ext === '.mjs' && typeFlag === 'commonjs') {
-    else
+      throw new ERR_ENTRY_TYPE_MISMATCH(
-      throw new ERR_UNKNOWN_FILE_EXTENSION(url.pathname);
+        fileURLToPath(url), ext, typeFlag, 'extension');
    }
    // Conflict between package scope type and --entry-type
    if (ext === '.js') {
      if (type === TYPE_MODULE && typeFlag === 'commonjs' ||
          type === TYPE_COMMONJS && typeFlag === 'module') {
        throw new ERR_ENTRY_TYPE_MISMATCH(
          fileURLToPath(url), ext, typeFlag, 'scope');
      }
    }
  }
  if (!format) {
    if (isMain && typeFlag)
      format = typeFlag;
    else if (isMain)
      format = type === TYPE_MODULE ? 'module' : 'commonjs';
    else
      throw new ERR_UNKNOWN_FILE_EXTENSION(fileURLToPath(url),
                                           fileURLToPath(parentURL));
  }
  return { url: `${url}`, format };
 }
 module.exports = resolve;
 // exported for tests
 module.exports.search = search;
--- a/lib/internal/modules/esm/loader.js
+++ b/lib/internal/modules/esm/loader.js
@ -11,10 +11,12 @@ const { URL } = require('url');
 const { validateString } = require('internal/validators');
 const ModuleMap = require('internal/modules/esm/module_map');
 const ModuleJob = require('internal/modules/esm/module_job');
 const defaultResolve = require('internal/modules/esm/default_resolve');
 const createDynamicModule = require(
  'internal/modules/esm/create_dynamic_module');
-const translators = require('internal/modules/esm/translators');
+const { translators } = require('internal/modules/esm/translators');
 const { ModuleWrap } = internalBinding('module_wrap');
 const FunctionBind = Function.call.bind(Function.prototype.bind);
@ -32,6 +34,9 @@ class Loader {
    // Registry of loaded modules, akin to `require.cache`
    this.moduleMap = new ModuleMap();
    // Map of already-loaded CJS modules to use
    this.cjsCache = new Map();
    // The resolver has the signature
    //   (specifier : string, parentURL : string, defaultResolve)
    //       -> Promise<{ url : string, format: string }>
@ -48,6 +53,8 @@ class Loader {
    // an object with the same keys as `exports`, whose values are get/set
    // functions for the actual exported values.
    this._dynamicInstantiate = undefined;
    // The index for assigning unique URLs to anonymous module evaluation
    this.evalIndex = 0;
  }
  async resolve(specifier, parentURL) {
@ -95,9 +102,25 @@ class Loader {
    return { url, format };
  }
  async eval(source, url = `eval:${++this.evalIndex}`) {
    const evalInstance = async (url) => {
      return {
        module: new ModuleWrap(source, url),
        reflect: undefined
      };
    };
    const job = new ModuleJob(this, url, evalInstance, false);
    this.moduleMap.set(url, job);
    const { module, result } = await job.run();
    return {
      namespace: module.namespace(),
      result
    };
  }
  async import(specifier, parent) {
    const job = await this.getModuleJob(specifier, parent);
-    const module = await job.run();
+    const { module } = await job.run();
    return module.namespace();
  }
@ -143,4 +166,4 @@ class Loader {
 Object.setPrototypeOf(Loader.prototype, null);
-module.exports = Loader;
+exports.Loader = Loader;
--- a/lib/internal/modules/esm/module_job.js
+++ b/lib/internal/modules/esm/module_job.js
@ -23,7 +23,7 @@ class ModuleJob {
    // This is a Promise<{ module, reflect }>, whose fields will be copied
    // onto `this` by `link()` below once it has been resolved.
-    this.modulePromise = moduleProvider(url, isMain);
+    this.modulePromise = moduleProvider.call(loader, url, isMain);
    this.module = undefined;
    this.reflect = undefined;
@ -101,8 +101,9 @@ class ModuleJob {
  async run() {
    const module = await this.instantiate();
-    module.evaluate(-1, false);
+    const timeout = -1;
-    return module;
+    const breakOnSigint = false;
    return { module, result: module.evaluate(timeout, breakOnSigint) };
  }
 }
 Object.setPrototypeOf(ModuleJob.prototype, null);
--- a/lib/internal/modules/esm/translators.js
+++ b/lib/internal/modules/esm/translators.js
@ -11,14 +11,10 @@ const internalURLModule = require('internal/url');
 const createDynamicModule = require(
  'internal/modules/esm/create_dynamic_module');
 const fs = require('fs');
 const { _makeLong } = require('path');
 const {
  SafeMap,
  JSON,
  FunctionPrototype,
  StringPrototype
 } = primordials;
-const { URL } = require('url');
+const { fileURLToPath, URL } = require('url');
 const { debuglog } = require('internal/util/debuglog');
 const { promisify } = require('internal/util');
 const esmLoader = require('internal/process/esm_loader');
@ -26,14 +22,13 @@ const {
  ERR_UNKNOWN_BUILTIN_MODULE
 } = require('internal/errors').codes;
 const readFileAsync = promisify(fs.readFile);
-const readFileSync = fs.readFileSync;
+const StringReplace = Function.call.bind(String.prototype.replace);
 const StringReplace = FunctionPrototype.call.bind(StringPrototype.replace);
 const JsonParse = JSON.parse;
 const debug = debuglog('esm');
 const translators = new SafeMap();
-module.exports = translators;
+exports.translators = translators;
 function initializeImportMeta(meta, { url }) {
  meta.url = url;
@ -45,7 +40,7 @@ async function importModuleDynamically(specifier, { url }) {
 }
 // Strategy for loading a standard JavaScript module
-translators.set('esm', async (url) => {
+translators.set('module', async function moduleStrategy(url) {
  const source = `${await readFileAsync(new URL(url))}`;
  debug(`Translating StandardModule ${url}`);
  const module = new ModuleWrap(stripShebang(source), url);
@ -62,9 +57,14 @@ translators.set('esm', async (url) => {
 // Strategy for loading a node-style CommonJS module
 const isWindows = process.platform === 'win32';
 const winSepRegEx = /\//g;
-translators.set('cjs', async (url, isMain) => {
+translators.set('commonjs', async function commonjsStrategy(url, isMain) {
  debug(`Translating CJSModule ${url}`);
  const pathname = internalURLModule.fileURLToPath(new URL(url));
  const cached = this.cjsCache.get(url);
  if (cached) {
    this.cjsCache.delete(url);
    return cached;
  }
  const module = CJSModule._cache[
    isWindows ? StringReplace(pathname, winSepRegEx, '\\') : pathname];
  if (module && module.loaded) {
@ -84,7 +84,7 @@ translators.set('cjs', async (url, isMain) => {
 // Strategy for loading a node builtin CommonJS module that isn't
 // through normal resolution
-translators.set('builtin', async (url) => {
+translators.set('builtin', async function builtinStrategy(url) {
  debug(`Translating BuiltinModule ${url}`);
  // Slice 'node:' scheme
  const id = url.slice(5);
@ -103,31 +103,38 @@ translators.set('builtin', async (url) => {
    });
 });
-// Strategy for loading a node native module
+// Strategy for loading a JSON file
-translators.set('addon', async (url) => {
+translators.set('json', async function jsonStrategy(url) {
-  debug(`Translating NativeModule ${url}`);
+  debug(`Translating JSONModule ${url}`);
  debug(`Loading JSONModule ${url}`);
  const pathname = fileURLToPath(url);
  const modulePath = isWindows ?
    StringReplace(pathname, winSepRegEx, '\\') : pathname;
  let module = CJSModule._cache[modulePath];
  if (module && module.loaded) {
    const exports = module.exports;
    return createDynamicModule(['default'], url, (reflect) => {
      reflect.exports.default.set(exports);
    });
  }
  const content = await readFileAsync(pathname, 'utf-8');
  try {
    const exports = JsonParse(stripBOM(content));
    module = {
      exports,
      loaded: true
    };
  } catch (err) {
    // TODO (BridgeAR): We could add a NodeCore error that wraps the JSON
    // parse error instead of just manipulating the original error message.
    // That would allow to add further properties and maybe additional
    // debugging information.
    err.message = pathname + ': ' + err.message;
    throw err;
  }
  CJSModule._cache[modulePath] = module;
  return createDynamicModule(['default'], url, (reflect) => {
-    debug(`Loading NativeModule ${url}`);
+    debug(`Parsing JSONModule ${url}`);
    const module = { exports: {} };
    const pathname = internalURLModule.fileURLToPath(new URL(url));
    process.dlopen(module, _makeLong(pathname));
    reflect.exports.default.set(module.exports);
  });
 });
 // Strategy for loading a JSON file
 translators.set('json', async (url) => {
  debug(`Translating JSONModule ${url}`);
  return createDynamicModule(['default'], url, (reflect) => {
    debug(`Loading JSONModule ${url}`);
    const pathname = internalURLModule.fileURLToPath(new URL(url));
    const content = readFileSync(pathname, 'utf8');
    try {
      const exports = JsonParse(stripBOM(content));
      reflect.exports.default.set(exports);
    } catch (err) {
      err.message = pathname + ': ' + err.message;
      throw err;
    }
  });
 });
--- a/lib/internal/process/esm_loader.js
+++ b/lib/internal/process/esm_loader.js
@ -3,16 +3,16 @@
 const {
  callbackMap,
 } = internalBinding('module_wrap');
 const { pathToFileURL } = require('internal/url');
 const Loader = require('internal/modules/esm/loader');
 const {
  wrapToModuleMap,
 } = require('internal/vm/source_text_module');
 const {
  ERR_VM_DYNAMIC_IMPORT_CALLBACK_MISSING,
 } = require('internal/errors').codes;
 const { Loader } = require('internal/modules/esm/loader');
 const { pathToFileURL } = require('internal/url');
 const {
  wrapToModuleMap,
 } = require('internal/vm/source_text_module');
 exports.initializeImportMetaObject = function(wrap, meta) {
  if (callbackMap.has(wrap)) {
    const { initializeImportMeta } = callbackMap.get(wrap);
@ -34,9 +34,7 @@ exports.importModuleDynamicallyCallback = async function(wrap, specifier) {
 };
 let loaderResolve;
-exports.loaderPromise = new Promise((resolve, reject) => {
+exports.loaderPromise = new Promise((resolve) => loaderResolve = resolve);
  loaderResolve = resolve;
 });
 exports.ESMLoader = undefined;
--- a/lib/internal/process/execution.js
+++ b/lib/internal/process/execution.js
@ -33,6 +33,24 @@ function tryGetCwd() {
  }
 }
 function evalModule(source) {
  const { decorateErrorStack } = require('internal/util');
  const asyncESM = require('internal/process/esm_loader');
  asyncESM.loaderPromise.then(async (loader) => {
    const { result } = await loader.eval(source);
    if (require('internal/options').getOptionValue('--print')) {
      console.log(result);
    }
  })
  .catch((e) => {
    decorateErrorStack(e);
    console.error(e);
    process.exit(1);
  });
  // Handle any nextTicks added in the first tick of the program.
  process._tickCallback();
 }
 function evalScript(name, body, breakFirstLine) {
  const CJSModule = require('internal/modules/cjs/loader');
  const { kVmBreakFirstLineSymbol } = require('internal/util');
@ -176,6 +194,7 @@ function readStdin(callback) {
 module.exports = {
  readStdin,
  tryGetCwd,
  evalModule,
  evalScript,
  fatalException: createFatalException(),
  setUncaughtExceptionCaptureCallback,
--- a/src/env.h
+++ b/src/env.h
@ -77,11 +77,13 @@ struct PackageConfig {
  enum class Exists { Yes, No };
  enum class IsValid { Yes, No };
  enum class HasMain { Yes, No };
  enum PackageType : uint32_t { None = 0, CommonJS, Module };
-  Exists exists;
+  const Exists exists;
-  IsValid is_valid;
+  const IsValid is_valid;
-  HasMain has_main;
+  const HasMain has_main;
-  std::string main;
+  const std::string main;
  const PackageType type;
 };
 }  // namespace loader
@ -141,6 +143,7 @@ constexpr size_t kFsStatsBufferLength = kFsStatsFieldsNumber * 2;
  V(channel_string, "channel")                                                 \
  V(chunks_sent_since_last_write_string, "chunksSentSinceLastWrite")           \
  V(code_string, "code")                                                       \
  V(commonjs_string, "commonjs")                                               \
  V(config_string, "config")                                                   \
  V(constants_string, "constants")                                             \
  V(crypto_dsa_string, "dsa")                                                  \
--- a/src/module_wrap.cc
+++ b/src/module_wrap.cc
@ -29,7 +29,6 @@ using v8::HandleScope;
 using v8::Integer;
 using v8::IntegrityLevel;
 using v8::Isolate;
 using v8::JSON;
 using v8::Just;
 using v8::Local;
 using v8::Maybe;
@ -46,7 +45,13 @@ using v8::String;
 using v8::Undefined;
 using v8::Value;
-static const char* const EXTENSIONS[] = {".mjs", ".js", ".json", ".node"};
+static const char* const EXTENSIONS[] = {
  ".mjs",
  ".cjs",
  ".js",
  ".json",
  ".node"
 };
 ModuleWrap::ModuleWrap(Environment* env,
                       Local<Object> object,
@ -471,100 +476,233 @@ std::string ReadFile(uv_file file) {
  return contents;
 }
-enum CheckFileOptions {
+enum DescriptorType {
-  LEAVE_OPEN_AFTER_CHECK,
+  FILE,
-  CLOSE_AFTER_CHECK
+  DIRECTORY,
  NONE
 };
-Maybe<uv_file> CheckFile(const std::string& path,
+// When DescriptorType cache is added, this can also return
-                         CheckFileOptions opt = CLOSE_AFTER_CHECK) {
+// Nothing for the "null" cache entries.
 inline Maybe<uv_file> OpenDescriptor(const std::string& path) {
  uv_fs_t fs_req;
  if (path.empty()) {
    return Nothing<uv_file>();
  }
  uv_file fd = uv_fs_open(nullptr, &fs_req, path.c_str(), O_RDONLY, 0, nullptr);
  uv_fs_req_cleanup(&fs_req);
-
+  if (fd < 0) return Nothing<uv_file>();
  if (fd < 0) {
    return Nothing<uv_file>();
  }
  uv_fs_fstat(nullptr, &fs_req, fd, nullptr);
  uint64_t is_directory = fs_req.statbuf.st_mode & S_IFDIR;
  uv_fs_req_cleanup(&fs_req);
  if (is_directory) {
    CHECK_EQ(0, uv_fs_close(nullptr, &fs_req, fd, nullptr));
    uv_fs_req_cleanup(&fs_req);
    return Nothing<uv_file>();
  }
  if (opt == CLOSE_AFTER_CHECK) {
    CHECK_EQ(0, uv_fs_close(nullptr, &fs_req, fd, nullptr));
    uv_fs_req_cleanup(&fs_req);
  }
  return Just(fd);
 }
 inline void CloseDescriptor(uv_file fd) {
  uv_fs_t fs_req;
  uv_fs_close(nullptr, &fs_req, fd, nullptr);
  uv_fs_req_cleanup(&fs_req);
 }
 inline DescriptorType CheckDescriptorAtFile(uv_file fd) {
  uv_fs_t fs_req;
  int rc = uv_fs_fstat(nullptr, &fs_req, fd, nullptr);
  if (rc == 0) {
    uint64_t is_directory = fs_req.statbuf.st_mode & S_IFDIR;
    uv_fs_req_cleanup(&fs_req);
    return is_directory ? DIRECTORY : FILE;
  }
  uv_fs_req_cleanup(&fs_req);
  return NONE;
 }
 // TODO(@guybedford): Add a DescriptorType cache layer here.
 // Should be directory based -> if path/to/dir doesn't exist
 // then the cache should early-fail any path/to/dir/file check.
 DescriptorType CheckDescriptorAtPath(const std::string& path) {
  Maybe<uv_file> fd = OpenDescriptor(path);
  if (fd.IsNothing()) return NONE;
  DescriptorType type = CheckDescriptorAtFile(fd.FromJust());
  CloseDescriptor(fd.FromJust());
  return type;
 }
 Maybe<std::string> ReadIfFile(const std::string& path) {
  Maybe<uv_file> fd = OpenDescriptor(path);
  if (fd.IsNothing()) return Nothing<std::string>();
  DescriptorType type = CheckDescriptorAtFile(fd.FromJust());
  if (type != FILE) return Nothing<std::string>();
  std::string source = ReadFile(fd.FromJust());
  CloseDescriptor(fd.FromJust());
  return Just(source);
 }
 using Exists = PackageConfig::Exists;
 using IsValid = PackageConfig::IsValid;
 using HasMain = PackageConfig::HasMain;
 using PackageType = PackageConfig::PackageType;
-const PackageConfig& GetPackageConfig(Environment* env,
+Maybe<const PackageConfig*> GetPackageConfig(Environment* env,
-                                      const std::string& path) {
+                                             const std::string& path,
                                             const URL& base) {
  auto existing = env->package_json_cache.find(path);
  if (existing != env->package_json_cache.end()) {
-    return existing->second;
+    const PackageConfig* pcfg = &existing->second;
    if (pcfg->is_valid == IsValid::No) {
      std::string msg = "Invalid JSON in '" + path +
        "' imported from " + base.ToFilePath();
      node::THROW_ERR_INVALID_PACKAGE_CONFIG(env, msg.c_str());
      return Nothing<const PackageConfig*>();
    }
    return Just(pcfg);
  }
-  Maybe<uv_file> check = CheckFile(path, LEAVE_OPEN_AFTER_CHECK);
+
-  if (check.IsNothing()) {
+  Maybe<std::string> source = ReadIfFile(path);
  if (source.IsNothing()) {
    auto entry = env->package_json_cache.emplace(path,
-        PackageConfig { Exists::No, IsValid::Yes, HasMain::No, "" });
+        PackageConfig { Exists::No, IsValid::Yes, HasMain::No, "",
-    return entry.first->second;
+                        PackageType::None });
    return Just(&entry.first->second);
  }
  std::string pkg_src = source.FromJust();
  Isolate* isolate = env->isolate();
  v8::HandleScope handle_scope(isolate);
  std::string pkg_src = ReadFile(check.FromJust());
  uv_fs_t fs_req;
  CHECK_EQ(0, uv_fs_close(nullptr, &fs_req, check.FromJust(), nullptr));
  uv_fs_req_cleanup(&fs_req);
  Local<String> src;
  if (!String::NewFromUtf8(isolate,
                           pkg_src.c_str(),
                           v8::NewStringType::kNormal,
                           pkg_src.length()).ToLocal(&src)) {
    auto entry = env->package_json_cache.emplace(path,
        PackageConfig { Exists::No, IsValid::Yes, HasMain::No, "" });
    return entry.first->second;
  }
  Local<Value> pkg_json_v;
  Local<Object> pkg_json;
  {
    Local<Value> src;
    Local<Value> pkg_json_v;
    Local<Context> context = env->context();
-  if (!JSON::Parse(env->context(), src).ToLocal(&pkg_json_v) ||
+    if (!ToV8Value(context, pkg_src).ToLocal(&src) ||
-      !pkg_json_v->ToObject(env->context()).ToLocal(&pkg_json)) {
+        !v8::JSON::Parse(context, src.As<String>()).ToLocal(&pkg_json_v) ||
-    auto entry = env->package_json_cache.emplace(path,
+        !pkg_json_v->ToObject(context).ToLocal(&pkg_json)) {
-        PackageConfig { Exists::Yes, IsValid::No, HasMain::No, "" });
+      env->package_json_cache.emplace(path,
-    return entry.first->second;
+          PackageConfig { Exists::Yes, IsValid::No, HasMain::No, "",
                          PackageType::None });
      std::string msg = "Invalid JSON in '" + path +
          "' imported from " + base.ToFilePath();
      node::THROW_ERR_INVALID_PACKAGE_CONFIG(env, msg.c_str());
      return Nothing<const PackageConfig*>();
    }
  }
  Local<Value> pkg_main;
  HasMain has_main = HasMain::No;
  std::string main_std;
  if (pkg_json->Get(env->context(), env->main_string()).ToLocal(&pkg_main)) {
-    has_main = HasMain::Yes;
+    if (pkg_main->IsString()) {
      has_main = HasMain::Yes;
    }
    Utf8Value main_utf8(isolate, pkg_main);
    main_std.assign(std::string(*main_utf8, main_utf8.length()));
  }
  PackageType pkg_type = PackageType::None;
  Local<Value> type_v;
  if (pkg_json->Get(env->context(), env->type_string()).ToLocal(&type_v)) {
    if (type_v->StrictEquals(env->module_string())) {
      pkg_type = PackageType::Module;
    } else if (type_v->StrictEquals(env->commonjs_string())) {
      pkg_type = PackageType::CommonJS;
    }
    // ignore unknown types for forwards compatibility
  }
  Local<Value> exports_v;
  if (pkg_json->Get(env->context(),
      env->exports_string()).ToLocal(&exports_v) &&
      (exports_v->IsObject() || exports_v->IsString() ||
      exports_v->IsBoolean())) {
    Persistent<Value> exports;
    exports.Reset(env->isolate(), exports_v);
    auto entry = env->package_json_cache.emplace(path,
        PackageConfig { Exists::Yes, IsValid::Yes, has_main, main_std,
                        pkg_type });
    return Just(&entry.first->second);
  }
  auto entry = env->package_json_cache.emplace(path,
-      PackageConfig { Exists::Yes, IsValid::Yes, has_main, main_std });
+      PackageConfig { Exists::Yes, IsValid::Yes, has_main, main_std,
-  return entry.first->second;
+                      pkg_type });
  return Just(&entry.first->second);
 }
 Maybe<const PackageConfig*> GetPackageScopeConfig(Environment* env,
                                                  const URL& resolved,
                                                  const URL& base) {
  URL pjson_url("./package.json", &resolved);
  while (true) {
    Maybe<const PackageConfig*> pkg_cfg =
        GetPackageConfig(env, pjson_url.ToFilePath(), base);
    if (pkg_cfg.IsNothing()) return pkg_cfg;
    if (pkg_cfg.FromJust()->exists == Exists::Yes) return pkg_cfg;
    URL last_pjson_url = pjson_url;
    pjson_url = URL("../package.json", pjson_url);
    // Terminates at root where ../package.json equals ../../package.json
    // (can't just check "/package.json" for Windows support).
    if (pjson_url.path() == last_pjson_url.path()) {
      auto entry = env->package_json_cache.emplace(pjson_url.ToFilePath(),
          PackageConfig { Exists::No, IsValid::Yes, HasMain::No, "",
                          PackageType::None });
      const PackageConfig* pcfg = &entry.first->second;
      return Just(pcfg);
    }
  }
 }
 /*
 * Legacy CommonJS main resolution:
 * 1. let M = pkg_url + (json main field)
 * 2. TRY(M, M.js, M.json, M.node)
 * 3. TRY(M/index.js, M/index.json, M/index.node)
 * 4. TRY(pkg_url/index.js, pkg_url/index.json, pkg_url/index.node)
 * 5. NOT_FOUND
 */
 inline bool FileExists(const URL& url) {
  return CheckDescriptorAtPath(url.ToFilePath()) == FILE;
 }
 Maybe<URL> LegacyMainResolve(const URL& pjson_url,
                             const PackageConfig& pcfg) {
  URL guess;
  if (pcfg.has_main == HasMain::Yes) {
    // Note: fs check redundances will be handled by Descriptor cache here.
    if (FileExists(guess = URL("./" + pcfg.main, pjson_url))) {
      return Just(guess);
    }
    if (FileExists(guess = URL("./" + pcfg.main + ".js", pjson_url))) {
      return Just(guess);
    }
    if (FileExists(guess = URL("./" + pcfg.main + ".json", pjson_url))) {
      return Just(guess);
    }
    if (FileExists(guess = URL("./" + pcfg.main + ".node", pjson_url))) {
      return Just(guess);
    }
    if (FileExists(guess = URL("./" + pcfg.main + "/index.js", pjson_url))) {
      return Just(guess);
    }
    // Such stat.
    if (FileExists(guess = URL("./" + pcfg.main + "/index.json", pjson_url))) {
      return Just(guess);
    }
    if (FileExists(guess = URL("./" + pcfg.main + "/index.node", pjson_url))) {
      return Just(guess);
    }
    // Fallthrough.
  }
  if (FileExists(guess = URL("./index.js", pjson_url))) {
    return Just(guess);
  }
  // So fs.
  if (FileExists(guess = URL("./index.json", pjson_url))) {
    return Just(guess);
  }
  if (FileExists(guess = URL("./index.node", pjson_url))) {
    return Just(guess);
  }
  // Not found.
  return Nothing<URL>();
 }
 enum ResolveExtensionsOptions {
@ -575,17 +713,14 @@ enum ResolveExtensionsOptions {
 template <ResolveExtensionsOptions options>
 Maybe<URL> ResolveExtensions(const URL& search) {
  if (options == TRY_EXACT_NAME) {
-    std::string filePath = search.ToFilePath();
+    if (FileExists(search)) {
    Maybe<uv_file> check = CheckFile(filePath);
    if (!check.IsNothing()) {
      return Just(search);
    }
  }
  for (const char* extension : EXTENSIONS) {
    URL guess(search.path() + extension, &search);
-    Maybe<uv_file> check = CheckFile(guess.ToFilePath());
+    if (FileExists(guess)) {
    if (!check.IsNothing()) {
      return Just(guess);
    }
  }
@ -597,93 +732,150 @@ inline Maybe<URL> ResolveIndex(const URL& search) {
  return ResolveExtensions<ONLY_VIA_EXTENSIONS>(URL("index", search));
 }
-Maybe<URL> ResolveMain(Environment* env, const URL& search) {
+Maybe<URL> FinalizeResolution(Environment* env,
-  URL pkg("package.json", &search);
+                              const URL& resolved,
-
+                              const URL& base) {
-  const PackageConfig& pjson =
+  if (env->options()->es_module_specifier_resolution == "node") {
-      GetPackageConfig(env, pkg.ToFilePath());
+    Maybe<URL> file = ResolveExtensions<TRY_EXACT_NAME>(resolved);
-  // Note invalid package.json should throw in resolver
+    if (!file.IsNothing()) {
-  // currently we silently ignore which is incorrect
+      return file;
-  if (pjson.exists == Exists::No ||
+    }
-      pjson.is_valid == IsValid::No ||
+    if (resolved.path().back() != '/') {
-      pjson.has_main == HasMain::No) {
+      file = ResolveIndex(URL(resolved.path() + "/", &base));
    } else {
      file = ResolveIndex(resolved);
    }
    if (!file.IsNothing()) {
      return file;
    }
    std::string msg = "Cannot find module '" + resolved.path() +
        "' imported from " + base.ToFilePath();
    node::THROW_ERR_MODULE_NOT_FOUND(env, msg.c_str());
    return Nothing<URL>();
  }
-  if (!ShouldBeTreatedAsRelativeOrAbsolutePath(pjson.main)) {
+
-    return Resolve(env, "./" + pjson.main, search, IgnoreMain);
+  const std::string& path = resolved.ToFilePath();
  if (CheckDescriptorAtPath(path) != FILE) {
    std::string msg = "Cannot find module '" + path +
        "' imported from " + base.ToFilePath();
    node::THROW_ERR_MODULE_NOT_FOUND(env, msg.c_str());
    return Nothing<URL>();
  }
-  return Resolve(env, pjson.main, search, IgnoreMain);
+
  return Just(resolved);
 }
-Maybe<URL> ResolveModule(Environment* env,
+Maybe<URL> PackageMainResolve(Environment* env,
-                         const std::string& specifier,
+                              const URL& pjson_url,
-                         const URL& base) {
+                              const PackageConfig& pcfg,
-  URL parent(".", base);
+                              const URL& base) {
-  URL dir("");
+  if (pcfg.exists == Exists::Yes) {
-  do {
+    if (pcfg.has_main == HasMain::Yes) {
-    dir = parent;
+      URL resolved(pcfg.main, pjson_url);
-    Maybe<URL> check =
+      const std::string& path = resolved.ToFilePath();
-        Resolve(env, "./node_modules/" + specifier, dir, CheckMain);
+      if (CheckDescriptorAtPath(path) == FILE) {
-    if (!check.IsNothing()) {
+        return Just(resolved);
      const size_t limit = specifier.find('/');
      const size_t spec_len =
          limit == std::string::npos ? specifier.length() :
                                       limit + 1;
      std::string chroot =
          dir.path() + "node_modules/" + specifier.substr(0, spec_len);
      if (check.FromJust().path().substr(0, chroot.length()) != chroot) {
        return Nothing<URL>();
      }
      return check;
    } else {
      // TODO(bmeck) PREVENT FALLTHROUGH
    }
-    parent = URL("..", &dir);
+    if (env->options()->es_module_specifier_resolution == "node") {
-  } while (parent.path() != dir.path());
+      if (pcfg.has_main == HasMain::Yes) {
        return FinalizeResolution(env, URL(pcfg.main, pjson_url), base);
      } else {
        return FinalizeResolution(env, URL("index", pjson_url), base);
      }
    }
    if (pcfg.type != PackageType::Module) {
      Maybe<URL> resolved = LegacyMainResolve(pjson_url, pcfg);
      if (!resolved.IsNothing()) {
        return resolved;
      }
    }
  }
  std::string msg = "Cannot find main entry point for '" +
      URL(".", pjson_url).ToFilePath() + "' imported from " +
      base.ToFilePath();
  node::THROW_ERR_MODULE_NOT_FOUND(env, msg.c_str());
  return Nothing<URL>();
 }
-Maybe<URL> ResolveDirectory(Environment* env,
+Maybe<URL> PackageResolve(Environment* env,
-                            const URL& search,
+                          const std::string& specifier,
-                            PackageMainCheck check_pjson_main) {
+                          const URL& base) {
-  if (check_pjson_main) {
+  size_t sep_index = specifier.find('/');
-    Maybe<URL> main = ResolveMain(env, search);
+  if (specifier[0] == '@' && (sep_index == std::string::npos ||
-    if (!main.IsNothing())
+      specifier.length() == 0)) {
-      return main;
+    std::string msg = "Invalid package name '" + specifier +
      "' imported from " + base.ToFilePath();
    node::THROW_ERR_INVALID_MODULE_SPECIFIER(env, msg.c_str());
    return Nothing<URL>();
  }
-  return ResolveIndex(search);
+  bool scope = false;
  if (specifier[0] == '@') {
    scope = true;
    sep_index = specifier.find('/', sep_index + 1);
  }
  std::string pkg_name = specifier.substr(0,
      sep_index == std::string::npos ? std::string::npos : sep_index);
  std::string pkg_subpath;
  if ((sep_index == std::string::npos ||
      sep_index == specifier.length() - 1)) {
    pkg_subpath = "";
  } else {
    pkg_subpath = "." + specifier.substr(sep_index);
  }
  URL pjson_url("./node_modules/" + pkg_name + "/package.json", &base);
  std::string pjson_path = pjson_url.ToFilePath();
  std::string last_path;
  do {
    DescriptorType check =
        CheckDescriptorAtPath(pjson_path.substr(0, pjson_path.length() - 13));
    if (check != DIRECTORY) {
      last_path = pjson_path;
      pjson_url = URL((scope ?
          "../../../../node_modules/" : "../../../node_modules/") +
          pkg_name + "/package.json", &pjson_url);
      pjson_path = pjson_url.ToFilePath();
      continue;
    }
    // Package match.
    Maybe<const PackageConfig*> pcfg = GetPackageConfig(env, pjson_path, base);
    // Invalid package configuration error.
    if (pcfg.IsNothing()) return Nothing<URL>();
    if (!pkg_subpath.length()) {
      return PackageMainResolve(env, pjson_url, *pcfg.FromJust(), base);
    } else {
      return FinalizeResolution(env, URL(pkg_subpath, pjson_url), base);
    }
    CHECK(false);
    // Cross-platform root check.
  } while (pjson_path.length() != last_path.length());
  std::string msg = "Cannot find package '" + pkg_name +
      "' imported from " + base.ToFilePath();
  node::THROW_ERR_MODULE_NOT_FOUND(env, msg.c_str());
  return Nothing<URL>();
 }
 }  // anonymous namespace
 Maybe<URL> Resolve(Environment* env,
                   const std::string& specifier,
-                   const URL& base,
+                   const URL& base) {
-                   PackageMainCheck check_pjson_main) {
+  // Order swapped from spec for minor perf gain.
-  URL pure_url(specifier);
+  // Ok since relative URLs cannot parse as URLs.
-  if (!(pure_url.flags() & URL_FLAGS_FAILED)) {
+  URL resolved;
    // just check existence, without altering
    Maybe<uv_file> check = CheckFile(pure_url.ToFilePath());
    if (check.IsNothing()) {
      return Nothing<URL>();
    }
    return Just(pure_url);
  }
  if (specifier.length() == 0) {
    return Nothing<URL>();
  }
  if (ShouldBeTreatedAsRelativeOrAbsolutePath(specifier)) {
-    URL resolved(specifier, base);
+    resolved = URL(specifier, base);
    Maybe<URL> file = ResolveExtensions<TRY_EXACT_NAME>(resolved);
    if (!file.IsNothing())
      return file;
    if (specifier.back() != '/') {
      resolved = URL(specifier + "/", base);
    }
    return ResolveDirectory(env, resolved, check_pjson_main);
  } else {
-    return ResolveModule(env, specifier, base);
+    URL pure_url(specifier);
    if (!(pure_url.flags() & URL_FLAGS_FAILED)) {
      resolved = pure_url;
    } else {
      return PackageResolve(env, specifier, base);
    }
  }
  return FinalizeResolution(env, resolved, base);
 }
 void ModuleWrap::Resolve(const FunctionCallbackInfo<Value>& args) {
@ -705,15 +897,40 @@ void ModuleWrap::Resolve(const FunctionCallbackInfo<Value>& args) {
        env, "second argument is not a URL string");
  }
-  Maybe<URL> result = node::loader::Resolve(env, specifier_std, url);
+  Maybe<URL> result =
-  if (result.IsNothing() || (result.FromJust().flags() & URL_FLAGS_FAILED)) {
+      node::loader::Resolve(env,
-    std::string msg = "Cannot find module " + specifier_std;
+                            specifier_std,
-    return node::THROW_ERR_MISSING_MODULE(env, msg.c_str());
+                            url);
  if (result.IsNothing()) {
    return;
  }
-  MaybeLocal<Value> obj = result.FromJust().ToObject(env);
+  URL resolution = result.FromJust();
-  if (!obj.IsEmpty())
+  CHECK(!(resolution.flags() & URL_FLAGS_FAILED));
-    args.GetReturnValue().Set(obj.ToLocalChecked());
+
  Local<Value> resolution_obj;
  if (resolution.ToObject(env).ToLocal(&resolution_obj))
    args.GetReturnValue().Set(resolution_obj);
 }
 void ModuleWrap::GetPackageType(const FunctionCallbackInfo<Value>& args) {
  Environment* env = Environment::GetCurrent(args);
  // module.getPackageType(url)
  CHECK_EQ(args.Length(), 1);
  CHECK(args[0]->IsString());
  Utf8Value url_utf8(env->isolate(), args[0]);
  URL url(*url_utf8, url_utf8.length());
  PackageType pkg_type = PackageType::None;
  Maybe<const PackageConfig*> pcfg =
      GetPackageScopeConfig(env, url, url);
  if (!pcfg.IsNothing()) {
    pkg_type = pcfg.FromJust()->type;
  }
  args.GetReturnValue().Set(Integer::New(env->isolate(), pkg_type));
 }
 static MaybeLocal<Promise> ImportModuleDynamically(
@ -849,6 +1066,7 @@ void ModuleWrap::Initialize(Local<Object> target,
  target->Set(env->context(), FIXED_ONE_BYTE_STRING(isolate, "ModuleWrap"),
              tpl->GetFunction(context).ToLocalChecked()).FromJust();
  env->SetMethod(target, "resolve", Resolve);
  env->SetMethod(target, "getPackageType", GetPackageType);
  env->SetMethod(target,
                 "setImportModuleDynamicallyCallback",
                 SetImportModuleDynamicallyCallback);
--- a/src/module_wrap.h
+++ b/src/module_wrap.h
@ -12,11 +12,6 @@
 namespace node {
 namespace loader {
 enum PackageMainCheck : bool {
    CheckMain = true,
    IgnoreMain = false
 };
 enum ScriptType : int {
  kScript,
  kModule,
@ -29,11 +24,6 @@ enum HostDefinedOptions : int {
  kLength = 10,
 };
 v8::Maybe<url::URL> Resolve(Environment* env,
                            const std::string& specifier,
                            const url::URL& base,
                            PackageMainCheck read_pkg_json = CheckMain);
 class ModuleWrap : public BaseObject {
 public:
  static const std::string EXTENSIONS[];
@ -75,6 +65,7 @@ class ModuleWrap : public BaseObject {
      const v8::FunctionCallbackInfo<v8::Value>& args);
  static void Resolve(const v8::FunctionCallbackInfo<v8::Value>& args);
  static void GetPackageType(const v8::FunctionCallbackInfo<v8::Value>& args);
  static void SetImportModuleDynamicallyCallback(
      const v8::FunctionCallbackInfo<v8::Value>& args);
  static void SetInitializeImportMetaObjectCallback(
--- a/src/node_errors.h
+++ b/src/node_errors.h
@ -45,12 +45,14 @@ void FatalException(v8::Isolate* isolate,
  V(ERR_CONSTRUCT_CALL_REQUIRED, Error)                                      \
  V(ERR_INVALID_ARG_VALUE, TypeError)                                        \
  V(ERR_INVALID_ARG_TYPE, TypeError)                                         \
  V(ERR_INVALID_MODULE_SPECIFIER, TypeError)                                 \
  V(ERR_INVALID_PACKAGE_CONFIG, SyntaxError)                                 \
  V(ERR_INVALID_TRANSFER_OBJECT, TypeError)                                  \
  V(ERR_MEMORY_ALLOCATION_FAILED, Error)                                     \
  V(ERR_MISSING_ARGS, TypeError)                                             \
  V(ERR_MISSING_MESSAGE_PORT_IN_TRANSFER_LIST, TypeError)                    \
  V(ERR_MISSING_MODULE, Error)                                               \
  V(ERR_MISSING_PLATFORM_FOR_WORKER, Error)                                  \
  V(ERR_MODULE_NOT_FOUND, Error)                                             \
  V(ERR_OUT_OF_RANGE, RangeError)                                            \
  V(ERR_SCRIPT_EXECUTION_INTERRUPTED, Error)                                 \
  V(ERR_SCRIPT_EXECUTION_TIMEOUT, Error)                                     \
--- a/src/node_options.cc
+++ b/src/node_options.cc
@ -107,6 +107,32 @@ void EnvironmentOptions::CheckOptions(std::vector<std::string>* errors) {
    errors->push_back("--loader requires --experimental-modules be enabled");
  }
  if (!module_type.empty()) {
    if (!experimental_modules) {
      errors->push_back("--entry-type requires "
                        "--experimental-modules to be enabled");
    }
    if (module_type != "commonjs" && module_type != "module") {
      errors->push_back("--entry-type must \"module\" or \"commonjs\"");
    }
  }
  if (experimental_json_modules && !experimental_modules) {
    errors->push_back("--experimental-json-modules requires "
                      "--experimental-modules be enabled");
  }
  if (!es_module_specifier_resolution.empty()) {
    if (!experimental_modules) {
      errors->push_back("--es-module-specifier-resolution requires "
                        "--experimental-modules be enabled");
    }
    if (es_module_specifier_resolution != "node" &&
        es_module_specifier_resolution != "explicit") {
      errors->push_back("invalid value for --es-module-specifier-resolution");
    }
  }
  if (syntax_check_only && has_eval_string) {
    errors->push_back("either --check or --eval can be used, not both");
  }
@ -214,6 +240,10 @@ DebugOptionsParser::DebugOptionsParser() {
 }
 EnvironmentOptionsParser::EnvironmentOptionsParser() {
  AddOption("--experimental-json-modules",
            "experimental JSON interop support for the ES Module loader",
            &EnvironmentOptions::experimental_json_modules,
            kAllowedInEnvironment);
  AddOption("--experimental-modules",
            "experimental ES Module support and caching modules",
            &EnvironmentOptions::experimental_modules,
@ -253,6 +283,11 @@ EnvironmentOptionsParser::EnvironmentOptionsParser() {
            "custom loader",
            &EnvironmentOptions::userland_loader,
            kAllowedInEnvironment);
  AddOption("--es-module-specifier-resolution",
            "Select extension resolution algorithm for es modules; "
            "either 'explicit' (default) or 'node'",
            &EnvironmentOptions::es_module_specifier_resolution,
            kAllowedInEnvironment);
  AddOption("--no-deprecation",
            "silence deprecation warnings",
            &EnvironmentOptions::no_deprecation,
@ -271,10 +306,12 @@ EnvironmentOptionsParser::EnvironmentOptionsParser() {
            kAllowedInEnvironment);
  AddOption("--preserve-symlinks",
            "preserve symbolic links when resolving",
-            &EnvironmentOptions::preserve_symlinks);
+            &EnvironmentOptions::preserve_symlinks,
            kAllowedInEnvironment);
  AddOption("--preserve-symlinks-main",
            "preserve symbolic links when resolving the main module",
-            &EnvironmentOptions::preserve_symlinks_main);
+            &EnvironmentOptions::preserve_symlinks_main,
            kAllowedInEnvironment);
  AddOption("--prof-process",
            "process V8 profiler output generated using --prof",
            &EnvironmentOptions::prof_process);
@ -301,6 +338,10 @@ EnvironmentOptionsParser::EnvironmentOptionsParser() {
            "show stack traces on process warnings",
            &EnvironmentOptions::trace_warnings,
            kAllowedInEnvironment);
  AddOption("--entry-type",
            "set module type name of the entry point",
            &EnvironmentOptions::module_type,
            kAllowedInEnvironment);
  AddOption("--check",
            "syntax check script without executing",
--- a/src/node_options.h
+++ b/src/node_options.h
@ -91,7 +91,10 @@ class DebugOptions : public Options {
 class EnvironmentOptions : public Options {
 public:
  bool abort_on_uncaught_exception = false;
  bool experimental_json_modules = false;
  bool experimental_modules = false;
  std::string es_module_specifier_resolution;
  std::string module_type;
  std::string experimental_policy;
  bool experimental_repl_await = false;
  bool experimental_vm_modules = false;
--- a/test/addons/hello-world-esm/binding.cc
+++ b/test/addons/hello-world-esm/binding.cc
@ -1,14 +0,0 @@
 #include <node.h>
 #include <v8.h>
 void Method(const v8::FunctionCallbackInfo<v8::Value>& args) {
  v8::Isolate* isolate = args.GetIsolate();
  args.GetReturnValue().Set(v8::String::NewFromUtf8(
        isolate, "world", v8::NewStringType::kNormal).ToLocalChecked());
 }
 void init(v8::Local<v8::Object> exports) {
  NODE_SET_METHOD(exports, "hello", Method);
 }
 NODE_MODULE(NODE_GYP_MODULE_NAME, init)
--- a/test/addons/hello-world-esm/binding.gyp
+++ b/test/addons/hello-world-esm/binding.gyp
@ -1,9 +0,0 @@
 {
  'targets': [
    {
      'target_name': 'binding',
      'sources': [ 'binding.cc' ],
      'includes': ['../common.gypi'],
    }
  ]
 }
--- a/test/addons/hello-world-esm/test.js
+++ b/test/addons/hello-world-esm/test.js
@ -1,20 +0,0 @@
 'use strict';
 const common = require('../../common');
 const assert = require('assert');
 const { spawnSync } = require('child_process');
 const { copyFileSync } = require('fs');
 const { join } = require('path');
 const buildDir = join(__dirname, 'build');
 copyFileSync(join(buildDir, common.buildType, 'binding.node'),
             join(buildDir, 'binding.node'));
 const result = spawnSync(process.execPath,
                         ['--experimental-modules', `${__dirname}/test.mjs`]);
 assert.ifError(result.error);
 // TODO: Uncomment this once ESM is no longer experimental.
 // assert.strictEqual(result.stderr.toString().trim(), '');
 assert.strictEqual(result.stdout.toString().trim(), 'binding.hello() = world');
--- a/test/addons/hello-world-esm/test.mjs
+++ b/test/addons/hello-world-esm/test.mjs
@ -1,6 +0,0 @@
 /* eslint-disable node-core/required-modules */
 import assert from 'assert';
 import binding from './build/binding.node';
 assert.strictEqual(binding.hello(), 'world');
 console.log('binding.hello() =', binding.hello());
--- a/test/common/index.mjs
+++ b/test/common/index.mjs
@ -1,6 +1,15 @@
 // Flags: --experimental-modules
 /* eslint-disable node-core/required-modules */
-import common from './index.js';
+
 import { createRequireFromPath } from 'module';
 import { fileURLToPath as toPath } from 'url';
 function createRequire(metaUrl) {
  return createRequireFromPath(toPath(metaUrl));
 }
 const require = createRequire(import.meta.url);
 const common = require('./index.js');
 const {
  isMainThread,
@ -91,5 +100,6 @@ export {
  getBufferSources,
  disableCrashOnUnhandledRejection,
  getTTYfd,
-  runWithInvalidFD
+  runWithInvalidFD,
  createRequire
 };
--- a/test/es-module/test-esm-basic-imports.mjs
+++ b/test/es-module/test-esm-basic-imports.mjs
@ -1,5 +1,6 @@
 // Flags: --experimental-modules
-import '../common';
+/* eslint-disable node-core/required-modules */
 import '../common/index.mjs';
 import assert from 'assert';
 import ok from '../fixtures/es-modules/test-esm-ok.mjs';
 import okShebang from './test-esm-shebang.mjs';
--- a/test/es-module/test-esm-cyclic-dynamic-import.mjs
+++ b/test/es-module/test-esm-cyclic-dynamic-import.mjs
@ -1,3 +1,4 @@
 // Flags: --experimental-modules
-import '../common';
+/* eslint-disable node-core/required-modules */
-import('./test-esm-cyclic-dynamic-import');
+import '../common/index.mjs';
 import('./test-esm-cyclic-dynamic-import.mjs');
--- a/test/es-module/test-esm-double-encoding.mjs
+++ b/test/es-module/test-esm-double-encoding.mjs
@ -1,6 +1,7 @@
 // Flags: --experimental-modules
-import '../common';
+/* eslint-disable node-core/required-modules */
 import '../common/index.mjs';
 // Assert we can import files with `%` in their pathname.
-import '../fixtures/es-modules/test-esm-double-encoding-native%2520.js';
+import '../fixtures/es-modules/test-esm-double-encoding-native%2520.mjs';
--- a/test/es-module/test-esm-dynamic-import.js
+++ b/test/es-module/test-esm-dynamic-import.js
@ -1,4 +1,5 @@
 // Flags: --experimental-modules
 'use strict';
 const common = require('../common');
 const assert = require('assert');
@ -17,7 +18,7 @@ function expectErrorProperty(result, propertyKey, value) {
 }
 function expectMissingModuleError(result) {
-  expectErrorProperty(result, 'code', 'MODULE_NOT_FOUND');
+  expectErrorProperty(result, 'code', 'ERR_MODULE_NOT_FOUND');
 }
 function expectOkNamespace(result) {
--- a/test/es-module/test-esm-encoded-path.mjs
+++ b/test/es-module/test-esm-encoded-path.mjs
@ -1,5 +1,6 @@
 // Flags: --experimental-modules
-import '../common';
+/* eslint-disable node-core/required-modules */
 import '../common/index.mjs';
 import assert from 'assert';
 // ./test-esm-ok.mjs
 import ok from '../fixtures/es-modules/test-%65%73%6d-ok.mjs';
--- a/test/es-module/test-esm-error-cache.js
+++ b/test/es-module/test-esm-error-cache.js
@ -1,11 +1,11 @@
 'use strict';
 // Flags: --experimental-modules
 'use strict';
 require('../common');
 const assert = require('assert');
-const file = '../fixtures/syntax/bad_syntax.js';
+const file = '../fixtures/syntax/bad_syntax.mjs';
 let error;
 (async () => {
--- a/test/es-module/test-esm-forbidden-globals.mjs
+++ b/test/es-module/test-esm-forbidden-globals.mjs
@ -1,5 +1,6 @@
 // Flags: --experimental-modules
-import '../common';
+/* eslint-disable node-core/required-modules */
 import '../common/index.mjs';
 // eslint-disable-next-line no-undef
 if (typeof arguments !== 'undefined') {
--- a/test/es-module/test-esm-import-meta.mjs
+++ b/test/es-module/test-esm-import-meta.mjs
@ -1,6 +1,7 @@
 // Flags: --experimental-modules
 /* eslint-disable node-core/required-modules */
-import '../common';
+import '../common/index.mjs';
 import assert from 'assert';
 assert.strictEqual(Object.getPrototypeOf(import.meta), null);
--- a/test/es-module/test-esm-json-cache.mjs
+++ b/test/es-module/test-esm-json-cache.mjs
@ -0,0 +1,26 @@
 // Flags: --experimental-modules --experimental-json-modules
 /* eslint-disable node-core/required-modules */
 import '../common/index.mjs';
 import { strictEqual, deepStrictEqual } from 'assert';
 import { createRequireFromPath as createRequire } from 'module';
 import { fileURLToPath as fromURL } from 'url';
 import mod from '../fixtures/es-modules/json-cache/mod.cjs';
 import another from '../fixtures/es-modules/json-cache/another.cjs';
 import test from '../fixtures/es-modules/json-cache/test.json';
 const require = createRequire(fromURL(import.meta.url));
 const modCjs = require('../fixtures/es-modules/json-cache/mod.cjs');
 const anotherCjs = require('../fixtures/es-modules/json-cache/another.cjs');
 const testCjs = require('../fixtures/es-modules/json-cache/test.json');
 strictEqual(mod.one, 1);
 strictEqual(another.one, 'zalgo');
 strictEqual(test.one, 'it comes');
 deepStrictEqual(mod, modCjs);
 deepStrictEqual(another, anotherCjs);
 deepStrictEqual(test, testCjs);
--- a/test/es-module/test-esm-json.mjs
+++ b/test/es-module/test-esm-json.mjs
@ -1,8 +1,9 @@
-// Flags: --experimental-modules
+// Flags: --experimental-modules --experimental-json-modules
-import '../common';
+/* eslint-disable node-core/required-modules */
 import assert from 'assert';
 import ok from '../fixtures/es-modules/test-esm-ok.mjs';
 import json from '../fixtures/es-modules/json.json';
-assert(ok);
+import '../common/index.mjs';
-assert.strictEqual(json.val, 42);
+import { strictEqual } from 'assert';
 import secret from '../fixtures/experimental.json';
 strictEqual(secret.ofLife, 42);
--- a/test/es-module/test-esm-live-binding.mjs
+++ b/test/es-module/test-esm-live-binding.mjs
@ -1,6 +1,7 @@
 // Flags: --experimental-modules
 /* eslint-disable node-core/required-modules */
-import '../common';
+import '../common/index.mjs';
 import assert from 'assert';
 import fs, { readFile, readFileSync } from 'fs';
--- a/test/es-module/test-esm-loader-invalid-format.mjs
+++ b/test/es-module/test-esm-loader-invalid-format.mjs
@ -1,5 +1,6 @@
 // Flags: --experimental-modules --loader ./test/fixtures/es-module-loaders/loader-invalid-format.mjs
-import { expectsError, mustCall } from '../common';
+/* eslint-disable node-core/required-modules */
 import { expectsError, mustCall } from '../common/index.mjs';
 import assert from 'assert';
 import('../fixtures/es-modules/test-esm-ok.mjs')
--- a/test/es-module/test-esm-loader-invalid-url.mjs
+++ b/test/es-module/test-esm-loader-invalid-url.mjs
@ -1,5 +1,7 @@
 // Flags: --experimental-modules --loader ./test/fixtures/es-module-loaders/loader-invalid-url.mjs
-import { expectsError, mustCall } from '../common';
+/* eslint-disable node-core/required-modules */
 import { expectsError, mustCall } from '../common/index.mjs';
 import assert from 'assert';
 import('../fixtures/es-modules/test-esm-ok.mjs')
--- a/test/es-module/test-esm-loader-missing-dynamic-instantiate-hook.mjs
+++ b/test/es-module/test-esm-loader-missing-dynamic-instantiate-hook.mjs
@ -1,6 +1,7 @@
 // Flags: --experimental-modules --loader ./test/fixtures/es-module-loaders/missing-dynamic-instantiate-hook.mjs
 /* eslint-disable node-core/required-modules */
-import { expectsError } from '../common';
+import { expectsError } from '../common/index.mjs';
 import('test').catch(expectsError({
  code: 'ERR_MISSING_DYNAMIC_INSTANTIATE_HOOK',
--- a/test/es-module/test-esm-loader-modulemap.js
+++ b/test/es-module/test-esm-loader-modulemap.js
@ -7,7 +7,7 @@
 const common = require('../common');
 const { URL } = require('url');
-const Loader = require('internal/modules/esm/loader');
+const { Loader } = require('internal/modules/esm/loader');
 const ModuleMap = require('internal/modules/esm/module_map');
 const ModuleJob = require('internal/modules/esm/module_job');
 const createDynamicModule = require(
--- a/test/es-module/test-esm-loader-search.js
+++ b/test/es-module/test-esm-loader-search.js
@ -5,13 +5,13 @@
 const common = require('../common');
-const { search } = require('internal/modules/esm/default_resolve');
+const resolve = require('internal/modules/esm/default_resolve');
 common.expectsError(
-  () => search('target', undefined),
+  () => resolve('target', undefined),
  {
-    code: 'ERR_MISSING_MODULE',
+    code: 'ERR_MODULE_NOT_FOUND',
    type: Error,
-    message: 'Cannot find module target'
+    message: /Cannot find package 'target'/
  }
 );
--- a/test/es-module/test-esm-main-lookup.mjs
+++ b/test/es-module/test-esm-main-lookup.mjs
@ -1,6 +1,26 @@
 // Flags: --experimental-modules
-import '../common';
+/* eslint-disable node-core/required-modules */
 import '../common/index.mjs';
 import assert from 'assert';
 import main from '../fixtures/es-modules/pjson-main';
-assert.strictEqual(main, 'main');
+async function main() {
  let mod;
  try {
    mod = await import('../fixtures/es-modules/pjson-main');
  } catch (e) {
    assert.strictEqual(e.code, 'ERR_MODULE_NOT_FOUND');
  }
  assert.strictEqual(mod, undefined);
  try {
    mod = await import('../fixtures/es-modules/pjson-main/main.mjs');
  } catch (e) {
    console.log(e);
    assert.fail();
  }
  assert.strictEqual(mod.main, 'main');
 }
 main();
--- a/test/es-module/test-esm-named-exports.mjs
+++ b/test/es-module/test-esm-named-exports.mjs
@ -1,5 +1,6 @@
 // Flags: --experimental-modules --loader ./test/fixtures/es-module-loaders/builtin-named-exports-loader.mjs
-import '../common';
+/* eslint-disable node-core/required-modules */
 import '../common/index.mjs';
 import { readFile } from 'fs';
 import assert from 'assert';
 import ok from '../fixtures/es-modules/test-esm-ok.mjs';
--- a/test/es-module/test-esm-namespace.mjs
+++ b/test/es-module/test-esm-namespace.mjs
@ -1,5 +1,7 @@
 // Flags: --experimental-modules
-import '../common';
+/* eslint-disable node-core/required-modules */
 import '../common/index.mjs';
 import * as fs from 'fs';
 import assert from 'assert';
 import Module from 'module';
--- a/test/es-module/test-esm-no-extension.js
+++ b/test/es-module/test-esm-no-extension.js
@ -0,0 +1,35 @@
 'use strict';
 const common = require('../common');
 const fixtures = require('../common/fixtures');
 const { spawn } = require('child_process');
 const assert = require('assert');
 const entry = fixtures.path('/es-modules/noext-esm');
 // Run a module that does not have extension
 // This is to ensure the --entry-type works as expected
 const child = spawn(process.execPath, [
  '--experimental-modules',
  '--entry-type=module',
  entry
 ]);
 let stderr = '';
 child.stderr.setEncoding('utf8');
 child.stderr.on('data', (data) => {
  stderr += data;
 });
 let stdout = '';
 child.stdout.setEncoding('utf8');
 child.stdout.on('data', (data) => {
  stdout += data;
 });
 child.on('close', common.mustCall((code, signal) => {
  assert.strictEqual(code, 0);
  assert.strictEqual(signal, null);
  assert.strictEqual(stdout, 'executed\n');
  assert.strictEqual(stderr, `(node:${child.pid}) ` +
      'ExperimentalWarning: The ESM module loader is experimental.\n');
 }));
--- a/test/es-module/test-esm-preserve-symlinks-not-found.mjs
+++ b/test/es-module/test-esm-preserve-symlinks-not-found.mjs
@ -1,3 +1,3 @@
 // Flags: --experimental-modules --loader ./test/fixtures/es-module-loaders/not-found-assert-loader.mjs
 /* eslint-disable node-core/required-modules */
-import './not-found';
+import './not-found.mjs';
--- a/test/es-module/test-esm-process.mjs
+++ b/test/es-module/test-esm-process.mjs
@ -1,5 +1,6 @@
 // Flags: --experimental-modules
-import '../common';
+/* eslint-disable node-core/required-modules */
 import '../common/index.mjs';
 import assert from 'assert';
 import process from 'process';
--- a/test/es-module/test-esm-require-cache.mjs
+++ b/test/es-module/test-esm-require-cache.mjs
@ -1,7 +1,12 @@
 // Flags: --experimental-modules
-import '../common';
+/* eslint-disable node-core/required-modules */
-import '../fixtures/es-module-require-cache/preload.js';
+import { createRequire } from '../common/index.mjs';
 import '../fixtures/es-module-require-cache/counter.js';
 import assert from 'assert';
 //
 const require = createRequire(import.meta.url);
 require('../fixtures/es-module-require-cache/preload.js');
 require('../fixtures/es-module-require-cache/counter.js');
 assert.strictEqual(global.counter, 1);
 delete global.counter;
--- a/test/es-module/test-esm-shared-loader-dep.mjs
+++ b/test/es-module/test-esm-shared-loader-dep.mjs
@ -1,7 +1,11 @@
 // Flags: --experimental-modules --loader ./test/fixtures/es-module-loaders/loader-shared-dep.mjs
-import '../common';
+/* eslint-disable node-core/required-modules */
 import { createRequire } from '../common/index.mjs';
 import assert from 'assert';
 import '../fixtures/es-modules/test-esm-ok.mjs';
 import dep from '../fixtures/es-module-loaders/loader-dep.js';
-assert.strictEqual(dep.format, 'esm');
+const require = createRequire(import.meta.url);
 const dep = require('../fixtures/es-module-loaders/loader-dep.js');
 assert.strictEqual(dep.format, 'module');
--- a/test/es-module/test-esm-shebang.mjs
+++ b/test/es-module/test-esm-shebang.mjs
@ -1,6 +1,7 @@
 #! }]) // isn't js
 // Flags: --experimental-modules
-import '../common';
+/* eslint-disable node-core/required-modules */
 import '../common/index.mjs';
 const isJs = true;
 export default isJs;
--- a/test/es-module/test-esm-snapshot.mjs
+++ b/test/es-module/test-esm-snapshot.mjs
@ -1,7 +1,8 @@
 // Flags: --experimental-modules
-import '../common';
+/* eslint-disable node-core/required-modules */
-import '../fixtures/es-modules/esm-snapshot-mutator';
+import '../common/index.mjs';
-import one from '../fixtures/es-modules/esm-snapshot';
+import '../fixtures/es-modules/esm-snapshot-mutator.js';
 import one from '../fixtures/es-modules/esm-snapshot.js';
 import assert from 'assert';
 assert.strictEqual(one, 1);
--- a/test/es-module/test-esm-specifiers.mjs
+++ b/test/es-module/test-esm-specifiers.mjs
@ -0,0 +1,35 @@
 // Flags: --experimental-modules --es-module-specifier-resolution=node
 import { mustNotCall } from '../common';
 import assert from 'assert';
 // commonJS index.js
 import commonjs from '../fixtures/es-module-specifiers/package-type-commonjs';
 // esm index.js
 import module from '../fixtures/es-module-specifiers/package-type-module';
 // Notice the trailing slash
 import success, { explicit, implicit, implicitModule, getImplicitCommonjs }
  from '../fixtures/es-module-specifiers/';
 assert.strictEqual(commonjs, 'commonjs');
 assert.strictEqual(module, 'module');
 assert.strictEqual(success, 'success');
 assert.strictEqual(explicit, 'esm');
 assert.strictEqual(implicit, 'esm');
 assert.strictEqual(implicitModule, 'esm');
 async function main() {
  try {
    await import('../fixtures/es-module-specifiers/do-not-exist.js');
  } catch (e) {
    // Files that do not exist should throw
    assert.strictEqual(e.name, 'Error');
  }
  try {
    await getImplicitCommonjs();
  } catch (e) {
    // Legacy loader cannot resolve .mjs automatically from main
    assert.strictEqual(e.name, 'Error');
  }
 }
 main().catch(mustNotCall);
--- a/test/es-module/test-esm-symlink-main.js
+++ b/test/es-module/test-esm-symlink-main.js
@ -9,7 +9,7 @@ const fs = require('fs');
 tmpdir.refresh();
 const realPath = path.resolve(__dirname, '../fixtures/es-modules/symlink.mjs');
-const symlinkPath = path.resolve(tmpdir.path, 'symlink.js');
+const symlinkPath = path.resolve(tmpdir.path, 'symlink.mjs');
 try {
  fs.symlinkSync(realPath, symlinkPath);
--- a/test/es-module/test-esm-symlink-type.js
+++ b/test/es-module/test-esm-symlink-type.js
@ -0,0 +1,77 @@
 'use strict';
 const common = require('../common');
 const fixtures = require('../common/fixtures');
 const path = require('path');
 const assert = require('assert');
 const exec = require('child_process').execFile;
 const fs = require('fs');
 const tmpdir = require('../common/tmpdir');
 tmpdir.refresh();
 const tmpDir = tmpdir.path;
 // Check that running the symlink executes the target as the correct type
 const symlinks = [
  {
    source: 'extensionless-symlink-to-mjs-file',
    target: fixtures.path('es-modules/mjs-file.mjs'),
    prints: '.mjs file',
    errorsWithPreserveSymlinksMain: false
  }, {
    source: 'extensionless-symlink-to-cjs-file',
    target: fixtures.path('es-modules/cjs-file.cjs'),
    prints: '.cjs file',
    errorsWithPreserveSymlinksMain: false
  }, {
    source: 'extensionless-symlink-to-file-in-module-scope',
    target: fixtures.path('es-modules/package-type-module/index.js'),
    prints: 'package-type-module',
    // The package scope of the symlinks' sources is commonjs, and this
    // symlink's target is a .js file in a module scope, so when the scope
    // is evaluated based on the source (commonjs) this esm file should error
    errorsWithPreserveSymlinksMain: true
  }, {
    source: 'extensionless-symlink-to-file-in-explicit-commonjs-scope',
    target: fixtures.path('es-modules/package-type-commonjs/index.js'),
    prints: 'package-type-commonjs',
    errorsWithPreserveSymlinksMain: false
  }, {
    source: 'extensionless-symlink-to-file-in-implicit-commonjs-scope',
    target: fixtures.path('es-modules/package-without-type/index.js'),
    prints: 'package-without-type',
    errorsWithPreserveSymlinksMain: false
  }
 ];
 symlinks.forEach((symlink) => {
  const mainPath = path.join(tmpDir, symlink.source);
  fs.symlinkSync(symlink.target, mainPath);
  const flags = [
    '--experimental-modules',
    '--experimental-modules --preserve-symlinks-main'
  ];
  flags.forEach((nodeOptions) => {
    const opts = {
      env: Object.assign({}, process.env, { NODE_OPTIONS: nodeOptions })
    };
    exec(process.execPath, [mainPath], opts, common.mustCall(
      (err, stdout) => {
        if (nodeOptions.includes('--preserve-symlinks-main')) {
          if (symlink.errorsWithPreserveSymlinksMain &&
              err.toString().includes('Error')) return;
          else if (!symlink.errorsWithPreserveSymlinksMain &&
                    stdout.includes(symlink.prints)) return;
          assert.fail(`For ${JSON.stringify(symlink)}, ${
            (symlink.errorsWithPreserveSymlinksMain) ?
              'failed to error' : 'errored unexpectedly'
          } with --preserve-symlinks-main`);
        } else {
          if (stdout.includes(symlink.prints)) return;
          assert.fail(`For ${JSON.stringify(symlink)}, failed to find ` +
            `${symlink.prints} in: <\n${stdout}\n>`);
        }
      }
    ));
  });
 });
--- a/test/es-module/test-esm-symlink.js
+++ b/test/es-module/test-esm-symlink.js
@ -12,8 +12,8 @@ const tmpDir = tmpdir.path;
 const entry = path.join(tmpDir, 'entry.mjs');
 const real = path.join(tmpDir, 'index.mjs');
-const link_absolute_path = path.join(tmpDir, 'absolute');
+const link_absolute_path = path.join(tmpDir, 'absolute.mjs');
-const link_relative_path = path.join(tmpDir, 'relative');
+const link_relative_path = path.join(tmpDir, 'relative.mjs');
 const link_ignore_extension = path.join(tmpDir,
                                        'ignore_extension.json');
 const link_directory = path.join(tmpDir, 'directory');
@ -22,15 +22,13 @@ fs.writeFileSync(real, 'export default [];');
 fs.writeFileSync(entry, `
 import assert from 'assert';
 import real from './index.mjs';
-import absolute from './absolute';
+import absolute from './absolute.mjs';
-import relative from './relative';
+import relative from './relative.mjs';
 import ignoreExtension from './ignore_extension.json';
 import directory from './directory';
 assert.strictEqual(absolute, real);
 assert.strictEqual(relative, real);
 assert.strictEqual(ignoreExtension, real);
 assert.strictEqual(directory, real);
 `);
 try {
--- a/test/es-module/test-esm-throw-undefined.mjs
+++ b/test/es-module/test-esm-throw-undefined.mjs
@ -1,11 +1,13 @@
 // Flags: --experimental-modules
-import '../common';
+/* eslint-disable node-core/required-modules */
 import '../common/index.mjs';
 import assert from 'assert';
 async function doTest() {
  await assert.rejects(
    async () => {
-      await import('../fixtures/es-module-loaders/throw-undefined');
+      await import('../fixtures/es-module-loaders/throw-undefined.mjs');
    },
    (e) => e === undefined
  );
--- a/test/es-module/test-esm-type-flag-errors.js
+++ b/test/es-module/test-esm-type-flag-errors.js
@ -0,0 +1,53 @@
 'use strict';
 const common = require('../common');
 const assert = require('assert');
 const exec = require('child_process').execFile;
 const mjsFile = require.resolve('../fixtures/es-modules/mjs-file.mjs');
 const cjsFile = require.resolve('../fixtures/es-modules/cjs-file.cjs');
 const packageWithoutTypeMain =
  require.resolve('../fixtures/es-modules/package-without-type/index.js');
 const packageTypeCommonJsMain =
  require.resolve('../fixtures/es-modules/package-type-commonjs/index.js');
 const packageTypeModuleMain =
  require.resolve('../fixtures/es-modules/package-type-module/index.js');
 // Check that running `node` without options works
 expect('', mjsFile, '.mjs file');
 expect('', cjsFile, '.cjs file');
 expect('', packageTypeModuleMain, 'package-type-module');
 expect('', packageTypeCommonJsMain, 'package-type-commonjs');
 expect('', packageWithoutTypeMain, 'package-without-type');
 // Check that running with --entry-type and no package.json "type" works
 expect('--entry-type=commonjs', packageWithoutTypeMain, 'package-without-type');
 expect('--entry-type=module', packageWithoutTypeMain, 'package-without-type');
 // Check that running with conflicting --entry-type flags throws errors
 expect('--entry-type=commonjs', mjsFile, 'ERR_ENTRY_TYPE_MISMATCH', true);
 expect('--entry-type=module', cjsFile, 'ERR_ENTRY_TYPE_MISMATCH', true);
 expect('--entry-type=commonjs', packageTypeModuleMain,
       'ERR_ENTRY_TYPE_MISMATCH', true);
 expect('--entry-type=module', packageTypeCommonJsMain,
       'ERR_ENTRY_TYPE_MISMATCH', true);
 function expect(opt = '', inputFile, want, wantsError = false) {
  // TODO: Remove when --experimental-modules is unflagged
  opt = `--experimental-modules ${opt}`;
  const argv = [inputFile];
  const opts = {
    env: Object.assign({}, process.env, { NODE_OPTIONS: opt }),
    maxBuffer: 1e6,
  };
  exec(process.execPath, argv, opts, common.mustCall((err, stdout, stderr) => {
    if (wantsError) {
      stdout = stderr;
    } else {
      assert.ifError(err);
    }
    if (stdout.includes(want)) return;
    const o = JSON.stringify(opt);
    assert.fail(`For ${o}, failed to find ${want} in: <\n${stdout}\n>`);
  }));
 }
--- a/test/es-module/test-esm-type-flag.mjs
+++ b/test/es-module/test-esm-type-flag.mjs
@ -0,0 +1,11 @@
 // Flags: --experimental-modules --entry-type=module
 /* eslint-disable node-core/required-modules */
 import cjs from '../fixtures/baz.js';
 import '../common/index.mjs';
 import { message } from '../fixtures/es-modules/message.mjs';
 import assert from 'assert';
 // Assert we loaded esm dependency as ".js" in this mode
 assert.strictEqual(message, 'A message');
 // Assert we loaded CommonJS dependency
 assert.strictEqual(cjs, 'perhaps I work');
--- a/test/fixtures/es-module-loaders/example-loader.mjs
+++ b/test/fixtures/es-module-loaders/example-loader.mjs
@ -29,6 +29,6 @@ export function resolve(specifier, parentModuleURL = baseURL /*, defaultResolve
  }
  return {
    url: resolved.href,
-    format: 'esm'
+    format: 'module'
  };
 }
--- a/test/fixtures/es-module-loaders/js-loader.mjs
+++ b/test/fixtures/es-module-loaders/js-loader.mjs
@ -15,6 +15,6 @@ export function resolve (specifier, base = baseURL) {
  const url = new URL(specifier, base).href;
  return {
    url,
-    format: 'esm'
+    format: 'module'
  };
 }
--- a/test/fixtures/es-module-loaders/loader-dep.js
+++ b/test/fixtures/es-module-loaders/loader-dep.js
@ -1 +1 @@
-exports.format = 'esm';
+exports.format = 'module';
--- a/test/fixtures/es-module-loaders/loader-invalid-url.mjs
+++ b/test/fixtures/es-module-loaders/loader-invalid-url.mjs
@ -1,3 +1,4 @@
 /* eslint-disable node-core/required-modules */
 export async function resolve(specifier, parentModuleURL, defaultResolve) {
  if (parentModuleURL && specifier === '../fixtures/es-modules/test-esm-ok.mjs') {
    return {
--- a/test/fixtures/es-module-loaders/loader-shared-dep.mjs
+++ b/test/fixtures/es-module-loaders/loader-shared-dep.mjs
@ -1,7 +1,11 @@
 import dep from './loader-dep.js';
 import assert from 'assert';
 import {createRequire} from '../../common/index.mjs';
 const require = createRequire(import.meta.url);
 const dep = require('./loader-dep.js');
 export function resolve(specifier, base, defaultResolve) {
-  assert.strictEqual(dep.format, 'esm');
+  assert.strictEqual(dep.format, 'module');
  return defaultResolve(specifier, base);
 }
--- a/test/fixtures/es-module-loaders/loader-with-dep.mjs
+++ b/test/fixtures/es-module-loaders/loader-with-dep.mjs
@ -1,4 +1,8 @@
-import dep from './loader-dep.js';
+import {createRequire} from '../../common/index.mjs';
 const require = createRequire(import.meta.url);
 const dep = require('./loader-dep.js');
 export function resolve (specifier, base, defaultResolve) {
  return {
    url: defaultResolve(specifier, base).url,
--- a/test/fixtures/es-module-loaders/not-found-assert-loader.mjs
+++ b/test/fixtures/es-module-loaders/not-found-assert-loader.mjs
@ -12,11 +12,11 @@ export async function resolve (specifier, base, defaultResolve) {
    await defaultResolve(specifier, base);
  }
  catch (e) {
-    assert.strictEqual(e.code, 'MODULE_NOT_FOUND');
+    assert.strictEqual(e.code, 'ERR_MODULE_NOT_FOUND');
    return {
      format: 'builtin',
      url: 'fs'
    };
  }
-  assert.fail(`Module resolution for ${specifier} should be throw MODULE_NOT_FOUND`);
+  assert.fail(`Module resolution for ${specifier} should be throw ERR_MODULE_NOT_FOUND`);
 }
--- a/test/fixtures/es-module-loaders/syntax-error-import.mjs
+++ b/test/fixtures/es-module-loaders/syntax-error-import.mjs
@ -1 +1 @@
-import { foo, notfound } from './module-named-exports';
+import { foo, notfound } from './module-named-exports.mjs';
--- a/test/fixtures/es-module-loaders/throw-undefined.mjs
+++ b/test/fixtures/es-module-loaders/throw-undefined.mjs
@ -1,3 +1,4 @@
 'use strict';
 /* eslint-disable node-core/required-modules */
 throw undefined;
--- a/test/fixtures/es-module-specifiers/index.mjs
+++ b/test/fixtures/es-module-specifiers/index.mjs
@ -0,0 +1,10 @@
 import explicit from 'explicit-main';
 import implicit from 'implicit-main';
 import implicitModule from 'implicit-main-type-module';
 function getImplicitCommonjs () {
  return import('implicit-main-type-commonjs');
 }
 export {explicit, implicit, implicitModule, getImplicitCommonjs};
 export default 'success';
--- a/test/fixtures/es-module-specifiers/node_modules/explicit-main/entry.mjs
+++ b/test/fixtures/es-module-specifiers/node_modules/explicit-main/entry.mjs
@ -0,0 +1 @@
 export default 'esm';
--- a/test/fixtures/es-module-specifiers/node_modules/explicit-main/package.json
+++ b/test/fixtures/es-module-specifiers/node_modules/explicit-main/package.json
@ -0,0 +1,3 @@
 {
  "main": "entry.mjs"
 }
--- a/test/fixtures/es-module-specifiers/node_modules/implicit-main-type-commonjs/entry.mjs
+++ b/test/fixtures/es-module-specifiers/node_modules/implicit-main-type-commonjs/entry.mjs
@ -0,0 +1 @@
 export default 'esm';
--- a/test/fixtures/es-module-specifiers/node_modules/implicit-main-type-commonjs/package.json
+++ b/test/fixtures/es-module-specifiers/node_modules/implicit-main-type-commonjs/package.json
@ -0,0 +1,4 @@
 {
  "main": "entry",
  "type": "commonjs"
 }
--- a/test/fixtures/es-module-specifiers/node_modules/implicit-main-type-module/entry.js
+++ b/test/fixtures/es-module-specifiers/node_modules/implicit-main-type-module/entry.js
@ -0,0 +1 @@
 export default 'nope';
--- a/test/fixtures/es-module-specifiers/node_modules/implicit-main-type-module/entry.mjs
+++ b/test/fixtures/es-module-specifiers/node_modules/implicit-main-type-module/entry.mjs
@ -0,0 +1 @@
 export default 'esm';
--- a/test/fixtures/es-module-specifiers/node_modules/implicit-main-type-module/package.json
+++ b/test/fixtures/es-module-specifiers/node_modules/implicit-main-type-module/package.json
@ -0,0 +1,4 @@
 {
  "main": "entry",
  "type": "module"
 }
--- a/test/fixtures/es-module-specifiers/node_modules/implicit-main/entry.js
+++ b/test/fixtures/es-module-specifiers/node_modules/implicit-main/entry.js
@ -0,0 +1 @@
 module.exports = 'cjs';
--- a/test/fixtures/es-module-specifiers/node_modules/implicit-main/entry.mjs
+++ b/test/fixtures/es-module-specifiers/node_modules/implicit-main/entry.mjs
@ -0,0 +1 @@
 export default 'esm';
--- a/test/fixtures/es-module-specifiers/node_modules/implicit-main/package.json
+++ b/test/fixtures/es-module-specifiers/node_modules/implicit-main/package.json
@ -0,0 +1,3 @@
 {
  "main": "entry"
 }
--- a/test/fixtures/es-module-specifiers/package-type-commonjs/a.js
+++ b/test/fixtures/es-module-specifiers/package-type-commonjs/a.js
@ -0,0 +1 @@
 module.exports = 'a';
--- a/test/fixtures/es-module-specifiers/package-type-commonjs/b.mjs
+++ b/test/fixtures/es-module-specifiers/package-type-commonjs/b.mjs
@ -0,0 +1 @@
 export const b = 'b';
--- a/test/fixtures/es-module-specifiers/package-type-commonjs/c.cjs
+++ b/test/fixtures/es-module-specifiers/package-type-commonjs/c.cjs
@ -0,0 +1,5 @@
 module.exports = {
  one: 1,
  two: 2,
  three: 3
 };
--- a/test/fixtures/es-module-specifiers/package-type-commonjs/index.mjs
+++ b/test/fixtures/es-module-specifiers/package-type-commonjs/index.mjs
@ -0,0 +1,21 @@
 // js file that is common.js
 import a from './a.js';
 // ESM with named export
 import {b} from './b.mjs';
 // import 'c.cjs';
 import cjs from './c.cjs';
 // proves cross boundary fun bits
 import jsAsEsm from '../package-type-module/a.js';
 // named export from core
 import {strictEqual, deepStrictEqual} from 'assert';
 strictEqual(a, jsAsEsm);
 strictEqual(b, 'b');
 deepStrictEqual(cjs, {
  one: 1,
  two: 2,
  three: 3
 });
 export default 'commonjs';
--- a/test/fixtures/es-module-specifiers/package-type-commonjs/package.json
+++ b/test/fixtures/es-module-specifiers/package-type-commonjs/package.json
@ -0,0 +1,3 @@
 {
  "type": "commonjs"
 }
--- a/test/fixtures/es-module-specifiers/package-type-module/a.js
+++ b/test/fixtures/es-module-specifiers/package-type-module/a.js
@ -0,0 +1 @@
 export default 'a'
--- a/test/fixtures/es-module-specifiers/package-type-module/b.mjs
+++ b/test/fixtures/es-module-specifiers/package-type-module/b.mjs
@ -0,0 +1 @@
 export const b = 'b';
--- a/test/fixtures/es-module-specifiers/package-type-module/c.cjs
+++ b/test/fixtures/es-module-specifiers/package-type-module/c.cjs
@ -0,0 +1,5 @@
 module.exports = {
  one: 1,
  two: 2,
  three: 3
 };
--- a/test/fixtures/es-module-specifiers/package-type-module/index.js
+++ b/test/fixtures/es-module-specifiers/package-type-module/index.js
@ -0,0 +1,21 @@
 // ESM with only default
 import a from './a.js';
 // ESM with named export
 import {b} from './b.mjs';
 // import 'c.cjs';
 import cjs from './c.cjs';
 // import across boundaries
 import jsAsCjs from '../package-type-commonjs/a.js'
 // named export from core
 import {strictEqual, deepStrictEqual} from 'assert';
 strictEqual(a, jsAsCjs);
 strictEqual(b, 'b');
 deepStrictEqual(cjs, {
  one: 1,
  two: 2,
  three: 3
 });
 export default 'module';
--- a/test/fixtures/es-module-specifiers/package-type-module/package.json
+++ b/test/fixtures/es-module-specifiers/package-type-module/package.json
@ -0,0 +1,3 @@
 {
  "type": "module"
 }
--- a/test/fixtures/es-module-specifiers/package.json
+++ b/test/fixtures/es-module-specifiers/package.json
@ -0,0 +1 @@
 {}
--- a/test/fixtures/es-modules/cjs-file.cjs
+++ b/test/fixtures/es-modules/cjs-file.cjs
@ -0,0 +1 @@
 console.log('.cjs file');
--- a/test/fixtures/es-modules/json-cache/another.cjs
+++ b/test/fixtures/es-modules/json-cache/another.cjs
@ -0,0 +1,7 @@
 const test = require('./test.json');
 module.exports = {
  ...test
 };
 test.one = 'it comes';
--- a/test/fixtures/es-modules/json-cache/mod.cjs
+++ b/test/fixtures/es-modules/json-cache/mod.cjs
@ -0,0 +1,7 @@
 const test = require('./test.json');
 module.exports = {
  ...test
 };
 test.one = 'zalgo';
--- a/test/fixtures/es-modules/json-cache/test.json
+++ b/test/fixtures/es-modules/json-cache/test.json
@ -0,0 +1,5 @@
 {
  "one": 1,
  "two": 2,
  "three": 3
 }
--- a/test/fixtures/es-modules/json.json
+++ b/test/fixtures/es-modules/json.json
@ -1,3 +0,0 @@
 {
  "val": 42
 }
--- a/test/fixtures/es-modules/loop.mjs
+++ b/test/fixtures/es-modules/loop.mjs
@ -1,4 +1,4 @@
-import { message } from './message';
+import { message } from './message.mjs';
 var t = 1;
 var k = 1;
--- a/test/fixtures/es-modules/mjs-file.mjs
+++ b/test/fixtures/es-modules/mjs-file.mjs
@ -0,0 +1 @@
 console.log('.mjs file');
--- a/Show More
+++ b/Show More
`@ -1 +1 @@`
	`exports.format = 'esm';`	`exports.format = 'module';`
`@ -1 +1 @@`
	`import { foo, notfound } from './module-named-exports';`	`import { foo, notfound } from './module-named-exports.mjs';`