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doc,module: clarify hook chain execution sequence

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PR-URL: https://github.com/nodejs/node/pull/51884
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Geoffrey Booth <webadmin@geoffreybooth.com>
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Jacob Smith 2024-03-02 15:33:25 +01:00 committed by GitHub
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1 changed files with 18 additions and 14 deletions
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32
doc/api/module.md
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@ -274,8 +274,8 @@ It's possible to call `register` more than once:
// entrypoint.mjs
import { register } from 'node:module';
register('./first.mjs', import.meta.url);
register('./second.mjs', import.meta.url);
register('./foo.mjs', import.meta.url);
register('./bar.mjs', import.meta.url);
await import('./my-app.mjs');
```
@ -285,20 +285,23 @@ const { register } = require('node:module');
const { pathToFileURL } = require('node:url');
const parentURL = pathToFileURL(__filename);
register('./first.mjs', parentURL);
register('./second.mjs', parentURL);
register('./foo.mjs', parentURL);
register('./bar.mjs', parentURL);
import('./my-app.mjs');
```
In this example, the registered hooks will form chains. If both `first.mjs` and
`second.mjs` define a `resolve` hook, both will be called, in the order they
were registered. The same applies to all the other hooks.
In this example, the registered hooks will form chains. These chains run
last-in, first out (LIFO). If both `foo.mjs` and `bar.mjs` define a `resolve`
hook, they will be called like so (note the right-to-left):
node's default ← `./foo.mjs` ← `./bar.mjs`
(starting with `./bar.mjs`, then `./foo.mjs`, then the Node.js default).
The same applies to all the other hooks.
The registered hooks also affect `register` itself. In this example,
`second.mjs` will be resolved and loaded per the hooks registered by
`first.mjs`. This allows for things like writing hooks in non-JavaScript
languages, so long as an earlier registered loader is one that transpiles into
JavaScript.
`bar.mjs` will be resolved and loaded via the hooks registered by `foo.mjs`
(because `foo`'s hooks will have already been added to the chain). This allows
for things like writing hooks in non-JavaScript languages, so long as
earlier registered hooks transpile into JavaScript.
The `register` method cannot be called from within the module that defines the
hooks.
@ -373,11 +376,11 @@ export async function load(url, context, nextLoad) {
}
```
Hooks are part of a chain, even if that chain consists of only one custom
(user-provided) hook and the default hook, which is always present. Hook
Hooks are part of a [chain][], even if that chain consists of only one
custom (user-provided) hook and the default hook, which is always present. Hook
functions nest: each one must always return a plain object, and chaining happens
as a result of each function calling `next<hookName>()`, which is a reference to
the subsequent loader's hook.
the subsequent loader's hook (in LIFO order).
A hook that returns a value lacking a required property triggers an exception. A
hook that returns without calling `next<hookName>()` _and_ without returning
@ -1060,6 +1063,7 @@ returned object contains the following keys:
[`register`]: #moduleregisterspecifier-parenturl-options
[`string`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String
[`util.TextDecoder`]: util.md#class-utiltextdecoder
[chain]: #chaining
[hooks]: #customization-hooks
[load hook]: #loadurl-context-nextload
[module wrapper]: modules.md#the-module-wrapper