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doc: restructure url.md

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PR-URL: https://github.com/nodejs/node/pull/12710
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
Reviewed-By: Daijiro Wachi <daijiro.wachi@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Gibson Fahnestock <gibfahn@gmail.com>
Reviewed-By: Sam Roberts <vieuxtech@gmail.com>
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James M Snell 2017-04-28 14:00:50 -07:00
parent 10754b60d0
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doc/api/url.md
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@ -15,371 +15,18 @@ A URL string is a structured string containing multiple meaningful components.
When parsed, a URL object is returned containing properties for each of these
components.
The following details each of the components of a parsed URL. The example
`'http://user:pass@sub.host.com:8080/p/a/t/h?query=string#hash'` is used to
illustrate each.
```txt
┌─────────────────────────────────────────────────────────────────────────────────┐
│ href │
├──────────┬┬───────────┬─────────────────────┬───────────────────────────┬───────┤
│ protocol ││ auth │ host │ path │ hash │
│ ││ ├──────────────┬──────┼──────────┬────────────────┤ │
│ ││ │ hostname │ port │ pathname │ search │ │
│ ││ │ │ │ ├─┬──────────────┤ │
│ ││ │ │ │ │ │ query │ │
" http: // user:pass @ sub.host.com : 8080 /p/a/t/h ? query=string #hash "
│ ││ │ │ │ │ │ │ │
└──────────┴┴───────────┴──────────────┴──────┴──────────┴─┴──────────────┴───────┘
(all spaces in the "" line should be ignored -- they are purely for formatting)
```
### urlObject.auth
The `auth` property is the username and password portion of the URL, also
referred to as "userinfo". This string subset follows the `protocol` and
double slashes (if present) and precedes the `host` component, delimited by an
ASCII "at sign" (`@`). The format of the string is `{username}[:{password}]`,
with the `[:{password}]` portion being optional.
For example: `'user:pass'`
### urlObject.hash
The `hash` property consists of the "fragment" portion of the URL including
the leading ASCII hash (`#`) character.
For example: `'#hash'`
### urlObject.host
The `host` property is the full lower-cased host portion of the URL, including
the `port` if specified.
For example: `'sub.host.com:8080'`
### urlObject.hostname
The `hostname` property is the lower-cased host name portion of the `host`
component *without* the `port` included.
For example: `'sub.host.com'`
### urlObject.href
The `href` property is the full URL string that was parsed with both the
`protocol` and `host` components converted to lower-case.
For example: `'http://user:pass@sub.host.com:8080/p/a/t/h?query=string#hash'`
### urlObject.path
The `path` property is a concatenation of the `pathname` and `search`
components.
For example: `'/p/a/t/h?query=string'`
No decoding of the `path` is performed.
### urlObject.pathname
The `pathname` property consists of the entire path section of the URL. This
is everything following the `host` (including the `port`) and before the start
of the `query` or `hash` components, delimited by either the ASCII question
mark (`?`) or hash (`#`) characters.
For example `'/p/a/t/h'`
No decoding of the path string is performed.
### urlObject.port
The `port` property is the numeric port portion of the `host` component.
For example: `'8080'`
### urlObject.protocol
The `protocol` property identifies the URL's lower-cased protocol scheme.
For example: `'http:'`
### urlObject.query
The `query` property is either the query string without the leading ASCII
question mark (`?`), or an object returned by the [`querystring`][] module's
`parse()` method. Whether the `query` property is a string or object is
determined by the `parseQueryString` argument passed to `url.parse()`.
For example: `'query=string'` or `{'query': 'string'}`
If returned as a string, no decoding of the query string is performed. If
returned as an object, both keys and values are decoded.
### urlObject.search
The `search` property consists of the entire "query string" portion of the
URL, including the leading ASCII question mark (`?`) character.
For example: `'?query=string'`
No decoding of the query string is performed.
### urlObject.slashes
The `slashes` property is a `boolean` with a value of `true` if two ASCII
forward-slash characters (`/`) are required following the colon in the
`protocol`.
## url.domainToASCII(domain)
<!-- YAML
added: v7.4.0
-->
> Stability: 1 - Experimental
* `domain` {string}
* Returns: {string}
Returns the [Punycode][] ASCII serialization of the `domain`. If `domain` is an
invalid domain, the empty string is returned.
It performs the inverse operation to [`url.domainToUnicode()`][].
```js
const url = require('url');
console.log(url.domainToASCII('español.com'));
// Prints xn--espaol-zwa.com
console.log(url.domainToASCII('中文.com'));
// Prints xn--fiq228c.com
console.log(url.domainToASCII('xn--iñvalid.com'));
// Prints an empty string
```
## url.domainToUnicode(domain)
<!-- YAML
added: v7.4.0
-->
> Stability: 1 - Experimental
* `domain` {string}
* Returns: {string}
Returns the Unicode serialization of the `domain`. If `domain` is an invalid
domain, the empty string is returned.
It performs the inverse operation to [`url.domainToASCII()`][].
```js
const url = require('url');
console.log(url.domainToUnicode('xn--espaol-zwa.com'));
// Prints español.com
console.log(url.domainToUnicode('xn--fiq228c.com'));
// Prints 中文.com
console.log(url.domainToUnicode('xn--iñvalid.com'));
// Prints an empty string
```
## url.format(urlObject)
<!-- YAML
added: v0.1.25
-->
* `urlObject` {Object|string} A URL object (as returned by `url.parse()` or
constructed otherwise). If a string, it is converted to an object by passing
it to `url.parse()`.
The `url.format()` method returns a formatted URL string derived from
`urlObject`.
If `urlObject` is not an object or a string, `url.parse()` will throw a
[`TypeError`][].
The formatting process operates as follows:
* A new empty string `result` is created.
* If `urlObject.protocol` is a string, it is appended as-is to `result`.
* Otherwise, if `urlObject.protocol` is not `undefined` and is not a string, an
[`Error`][] is thrown.
* For all string values of `urlObject.protocol` that *do not end* with an ASCII
colon (`:`) character, the literal string `:` will be appended to `result`.
* If either of the following conditions is true, then the literal string `//`
will be appended to `result`:
* `urlObject.slashes` property is true;
* `urlObject.protocol` begins with `http`, `https`, `ftp`, `gopher`, or
`file`;
* If the value of the `urlObject.auth` property is truthy, and either
`urlObject.host` or `urlObject.hostname` are not `undefined`, the value of
`urlObject.auth` will be coerced into a string and appended to `result`
followed by the literal string `@`.
* If the `urlObject.host` property is `undefined` then:
* If the `urlObject.hostname` is a string, it is appended to `result`.
* Otherwise, if `urlObject.hostname` is not `undefined` and is not a string,
an [`Error`][] is thrown.
* If the `urlObject.port` property value is truthy, and `urlObject.hostname`
is not `undefined`:
* The literal string `:` is appended to `result`, and
* The value of `urlObject.port` is coerced to a string and appended to
`result`.
* Otherwise, if the `urlObject.host` property value is truthy, the value of
`urlObject.host` is coerced to a string and appended to `result`.
* If the `urlObject.pathname` property is a string that is not an empty string:
* If the `urlObject.pathname` *does not start* with an ASCII forward slash
(`/`), then the literal string '/' is appended to `result`.
* The value of `urlObject.pathname` is appended to `result`.
* Otherwise, if `urlObject.pathname` is not `undefined` and is not a string, an
[`Error`][] is thrown.
* If the `urlObject.search` property is `undefined` and if the `urlObject.query`
property is an `Object`, the literal string `?` is appended to `result`
followed by the output of calling the [`querystring`][] module's `stringify()`
method passing the value of `urlObject.query`.
* Otherwise, if `urlObject.search` is a string:
* If the value of `urlObject.search` *does not start* with the ASCII question
mark (`?`) character, the literal string `?` is appended to `result`.
* The value of `urlObject.search` is appended to `result`.
* Otherwise, if `urlObject.search` is not `undefined` and is not a string, an
[`Error`][] is thrown.
* If the `urlObject.hash` property is a string:
* If the value of `urlObject.hash` *does not start* with the ASCII hash (`#`)
character, the literal string `#` is appended to `result`.
* The value of `urlObject.hash` is appended to `result`.
* Otherwise, if the `urlObject.hash` property is not `undefined` and is not a
string, an [`Error`][] is thrown.
* `result` is returned.
## url.format(URL[, options])
<!-- YAML
added: v7.6.0
-->
* `URL` {URL} A [WHATWG URL][] object
* `options` {Object}
* `auth` {boolean} `true` if the serialized URL string should include the
username and password, `false` otherwise. Defaults to `true`.
* `fragment` {boolean} `true` if the serialized URL string should include the
fragment, `false` otherwise. Defaults to `true`.
* `search` {boolean} `true` if the serialized URL string should include the
search query, `false` otherwise. Defaults to `true`.
* `unicode` {boolean} `true` if Unicode characters appearing in the host
component of the URL string should be encoded directly as opposed to being
Punycode encoded. Defaults to `false`.
Returns a customizable serialization of a URL String representation of a
[WHATWG URL][] object.
The URL object has both a `toString()` method and `href` property that return
string serializations of the URL. These are not, however, customizable in
any way. The `url.format(URL[, options])` method allows for basic customization
of the output.
For example:
```js
const myURL = new URL('https://a:b@你好你好?abc#foo');
console.log(myURL.href);
// Prints https://a:b@xn--6qqa088eba/?abc#foo
console.log(myURL.toString());
// Prints https://a:b@xn--6qqa088eba/?abc#foo
console.log(url.format(myURL, {fragment: false, unicode: true, auth: false}));
// Prints 'https://你好你好?abc'
```
## url.parse(urlString[, parseQueryString[, slashesDenoteHost]])
<!-- YAML
added: v0.1.25
-->
* `urlString` {string} The URL string to parse.
* `parseQueryString` {boolean} If `true`, the `query` property will always
be set to an object returned by the [`querystring`][] module's `parse()`
method. If `false`, the `query` property on the returned URL object will be an
unparsed, undecoded string. Defaults to `false`.
* `slashesDenoteHost` {boolean} If `true`, the first token after the literal
string `//` and preceding the next `/` will be interpreted as the `host`.
For instance, given `//foo/bar`, the result would be
`{host: 'foo', pathname: '/bar'}` rather than `{pathname: '//foo/bar'}`.
Defaults to `false`.
The `url.parse()` method takes a URL string, parses it, and returns a URL
object.
A `TypeError` is thrown if `urlString` is not a string.
A `URIError` is thrown if the `auth` property is present but cannot be decoded.
## url.resolve(from, to)
<!-- YAML
added: v0.1.25
changes:
- version: v6.6.0
pr-url: https://github.com/nodejs/node/pull/8215
description: The `auth` fields are now kept intact when `from` and `to`
refer to the same host.
- version: v6.5.0, v4.6.2
pr-url: https://github.com/nodejs/node/pull/8214
description: The `port` field is copied correctly now.
- version: v6.0.0
pr-url: https://github.com/nodejs/node/pull/1480
description: The `auth` fields is cleared now the `to` parameter
contains a hostname.
-->
* `from` {string} The Base URL being resolved against.
* `to` {string} The HREF URL being resolved.
The `url.resolve()` method resolves a target URL relative to a base URL in a
manner similar to that of a Web browser resolving an anchor tag HREF.
For example:
```js
url.resolve('/one/two/three', 'four'); // '/one/two/four'
url.resolve('http://example.com/', '/one'); // 'http://example.com/one'
url.resolve('http://example.com/one', '/two'); // 'http://example.com/two'
```
## Escaped Characters
URLs are only permitted to contain a certain range of characters. Spaces (`' '`)
and the following characters will be automatically escaped in the
properties of URL objects:
```txt
< > " ` \r \n \t { } | \ ^ '
```
For example, the ASCII space character (`' '`) is encoded as `%20`. The ASCII
forward slash (`/`) character is encoded as `%3C`.
## The WHATWG URL API
<!-- YAML
added: v7.0.0
-->
The `url` module provides an implementation of the [WHATWG URL Standard][] as
an alternative to the existing `url.parse()` API.
```js
const URL = require('url').URL;
const myURL = new URL('https://example.org/foo');
console.log(myURL.href); // https://example.org/foo
console.log(myURL.protocol); // https:
console.log(myURL.hostname); // example.org
console.log(myURL.pathname); // /foo
```
*Note*: Using the `delete` keyword (e.g. `delete myURL.protocol`,
`delete myURL.pathname`, etc) has no effect but will still return `true`.
A comparison between this API and `url.parse()` is given below. Above the URL
`'http://user:pass@sub.host.com:8080/p/a/t/h?query=string#hash'`, properties of an
object returned by `url.parse()` are shown. Below it are properties of a WHATWG
`URL` object.
The `url` module provides two APIs for working with URLs: a legacy API that is
Node.js specific, and a newer API that implements the same
[WHATWG URL Standard][] used by web browsers.
*Note*: While the Legacy API has not been deprecated, it is maintained solely
for backwards compatibility with existing applications. New application code
should use the WHATWG API.
A comparison between the WHATWG and Legacy APIs is provided below. Above the URL
`'http://user:pass@sub.host.com:8080/p/a/t/h?query=string#hash'`, properties of
an object returned by the legacy `url.parse()` are shown. Below it are
properties of a WHATWG `URL` object.
*Note*: WHATWG URL's `origin` property includes `protocol` and `host`, but not
`username` or `password`.
@ -393,7 +40,7 @@ object returned by `url.parse()` are shown. Below it are properties of a WHATWG
│ │ │ │ hostname │ port │ pathname │ search │ │
│ │ │ │ │ │ ├─┬──────────────┤ │
│ │ │ │ │ │ │ │ query │ │
" http: // user : pass @ sub.host.com : 8080 /p/a/t/h ? query=string #hash "
" https: // user : pass @ sub.host.com : 8080 /p/a/t/h ? query=string #hash "
│ │ │ │ │ hostname │ port │ │ │ │
│ │ │ │ ├──────────────┴──────┤ │ │ │
│ protocol │ │ username │ password │ host │ │ │ │
@ -405,6 +52,35 @@ object returned by `url.parse()` are shown. Below it are properties of a WHATWG
(all spaces in the "" line should be ignored -- they are purely for formatting)
```
Parsing the URL string using the WHATWG API:
```js
const URL = require('url').URL;
const myURL =
new URL('https://user:pass@sub.host.com:8080/p/a/t/h?query=string#hash');
```
*Note*: In Web Browsers, the WHATWG `URL` class is a global that is always
available. In Node.js, however, the `URL` class must be accessed via
`require('url').URL`.
Parsing the URL string using the Legacy API:
```js
const url = require('url');
const myURL =
url.parse('https://user:pass@sub.host.com:8080/p/a/t/h?query=string#hash');
```
## The WHATWG URL API
<!-- YAML
added: v7.0.0
-->
*Note*: Using the `delete` keyword on `URL` objects (e.g.
`delete myURL.protocol`, `delete myURL.pathname`, etc) has no effect but will
still return `true`.
### Class: URL
#### Constructor: new URL(input[, base])
@ -1058,15 +734,342 @@ for (const [name, value] of params) {
// xyz baz
```
### url.domainToASCII(domain)
<!-- YAML
added: v7.4.0
-->
* `domain` {string}
* Returns: {string}
Returns the [Punycode][] ASCII serialization of the `domain`. If `domain` is an
invalid domain, the empty string is returned.
It performs the inverse operation to [`url.domainToUnicode()`][].
```js
const url = require('url');
console.log(url.domainToASCII('español.com'));
// Prints xn--espaol-zwa.com
console.log(url.domainToASCII('中文.com'));
// Prints xn--fiq228c.com
console.log(url.domainToASCII('xn--iñvalid.com'));
// Prints an empty string
```
### url.domainToUnicode(domain)
<!-- YAML
added: v7.4.0
-->
* `domain` {string}
* Returns: {string}
Returns the Unicode serialization of the `domain`. If `domain` is an invalid
domain, the empty string is returned.
It performs the inverse operation to [`url.domainToASCII()`][].
```js
const url = require('url');
console.log(url.domainToUnicode('xn--espaol-zwa.com'));
// Prints español.com
console.log(url.domainToUnicode('xn--fiq228c.com'));
// Prints 中文.com
console.log(url.domainToUnicode('xn--iñvalid.com'));
// Prints an empty string
```
### url.format(URL[, options])
<!-- YAML
added: v7.6.0
-->
* `URL` {URL} A [WHATWG URL][] object
* `options` {Object}
* `auth` {boolean} `true` if the serialized URL string should include the
username and password, `false` otherwise. Defaults to `true`.
* `fragment` {boolean} `true` if the serialized URL string should include the
fragment, `false` otherwise. Defaults to `true`.
* `search` {boolean} `true` if the serialized URL string should include the
search query, `false` otherwise. Defaults to `true`.
* `unicode` {boolean} `true` if Unicode characters appearing in the host
component of the URL string should be encoded directly as opposed to being
Punycode encoded. Defaults to `false`.
Returns a customizable serialization of a URL String representation of a
[WHATWG URL][] object.
The URL object has both a `toString()` method and `href` property that return
string serializations of the URL. These are not, however, customizable in
any way. The `url.format(URL[, options])` method allows for basic customization
of the output.
For example:
```js
const myURL = new URL('https://a:b@你好你好?abc#foo');
console.log(myURL.href);
// Prints https://a:b@xn--6qqa088eba/?abc#foo
console.log(myURL.toString());
// Prints https://a:b@xn--6qqa088eba/?abc#foo
console.log(url.format(myURL, {fragment: false, unicode: true, auth: false}));
// Prints 'https://你好你好?abc'
```
## Legacy URL API
### Legacy urlObject
The legacy urlObject (`require('url').Url`) is created and returned by the
`url.parse()` function.
#### urlObject.auth
The `auth` property is the username and password portion of the URL, also
referred to as "userinfo". This string subset follows the `protocol` and
double slashes (if present) and precedes the `host` component, delimited by an
ASCII "at sign" (`@`). The format of the string is `{username}[:{password}]`,
with the `[:{password}]` portion being optional.
For example: `'user:pass'`
#### urlObject.hash
The `hash` property consists of the "fragment" portion of the URL including
the leading ASCII hash (`#`) character.
For example: `'#hash'`
#### urlObject.host
The `host` property is the full lower-cased host portion of the URL, including
the `port` if specified.
For example: `'sub.host.com:8080'`
#### urlObject.hostname
The `hostname` property is the lower-cased host name portion of the `host`
component *without* the `port` included.
For example: `'sub.host.com'`
#### urlObject.href
The `href` property is the full URL string that was parsed with both the
`protocol` and `host` components converted to lower-case.
For example: `'http://user:pass@sub.host.com:8080/p/a/t/h?query=string#hash'`
#### urlObject.path
The `path` property is a concatenation of the `pathname` and `search`
components.
For example: `'/p/a/t/h?query=string'`
No decoding of the `path` is performed.
#### urlObject.pathname
The `pathname` property consists of the entire path section of the URL. This
is everything following the `host` (including the `port`) and before the start
of the `query` or `hash` components, delimited by either the ASCII question
mark (`?`) or hash (`#`) characters.
For example `'/p/a/t/h'`
No decoding of the path string is performed.
#### urlObject.port
The `port` property is the numeric port portion of the `host` component.
For example: `'8080'`
#### urlObject.protocol
The `protocol` property identifies the URL's lower-cased protocol scheme.
For example: `'http:'`
#### urlObject.query
The `query` property is either the query string without the leading ASCII
question mark (`?`), or an object returned by the [`querystring`][] module's
`parse()` method. Whether the `query` property is a string or object is
determined by the `parseQueryString` argument passed to `url.parse()`.
For example: `'query=string'` or `{'query': 'string'}`
If returned as a string, no decoding of the query string is performed. If
returned as an object, both keys and values are decoded.
#### urlObject.search
The `search` property consists of the entire "query string" portion of the
URL, including the leading ASCII question mark (`?`) character.
For example: `'?query=string'`
No decoding of the query string is performed.
#### urlObject.slashes
The `slashes` property is a `boolean` with a value of `true` if two ASCII
forward-slash characters (`/`) are required following the colon in the
`protocol`.
### url.format(urlObject)
<!-- YAML
added: v0.1.25
-->
* `urlObject` {Object|string} A URL object (as returned by `url.parse()` or
constructed otherwise). If a string, it is converted to an object by passing
it to `url.parse()`.
The `url.format()` method returns a formatted URL string derived from
`urlObject`.
If `urlObject` is not an object or a string, `url.parse()` will throw a
[`TypeError`][].
The formatting process operates as follows:
* A new empty string `result` is created.
* If `urlObject.protocol` is a string, it is appended as-is to `result`.
* Otherwise, if `urlObject.protocol` is not `undefined` and is not a string, an
[`Error`][] is thrown.
* For all string values of `urlObject.protocol` that *do not end* with an ASCII
colon (`:`) character, the literal string `:` will be appended to `result`.
* If either of the following conditions is true, then the literal string `//`
will be appended to `result`:
* `urlObject.slashes` property is true;
* `urlObject.protocol` begins with `http`, `https`, `ftp`, `gopher`, or
`file`;
* If the value of the `urlObject.auth` property is truthy, and either
`urlObject.host` or `urlObject.hostname` are not `undefined`, the value of
`urlObject.auth` will be coerced into a string and appended to `result`
followed by the literal string `@`.
* If the `urlObject.host` property is `undefined` then:
* If the `urlObject.hostname` is a string, it is appended to `result`.
* Otherwise, if `urlObject.hostname` is not `undefined` and is not a string,
an [`Error`][] is thrown.
* If the `urlObject.port` property value is truthy, and `urlObject.hostname`
is not `undefined`:
* The literal string `:` is appended to `result`, and
* The value of `urlObject.port` is coerced to a string and appended to
`result`.
* Otherwise, if the `urlObject.host` property value is truthy, the value of
`urlObject.host` is coerced to a string and appended to `result`.
* If the `urlObject.pathname` property is a string that is not an empty string:
* If the `urlObject.pathname` *does not start* with an ASCII forward slash
(`/`), then the literal string '/' is appended to `result`.
* The value of `urlObject.pathname` is appended to `result`.
* Otherwise, if `urlObject.pathname` is not `undefined` and is not a string, an
[`Error`][] is thrown.
* If the `urlObject.search` property is `undefined` and if the `urlObject.query`
property is an `Object`, the literal string `?` is appended to `result`
followed by the output of calling the [`querystring`][] module's `stringify()`
method passing the value of `urlObject.query`.
* Otherwise, if `urlObject.search` is a string:
* If the value of `urlObject.search` *does not start* with the ASCII question
mark (`?`) character, the literal string `?` is appended to `result`.
* The value of `urlObject.search` is appended to `result`.
* Otherwise, if `urlObject.search` is not `undefined` and is not a string, an
[`Error`][] is thrown.
* If the `urlObject.hash` property is a string:
* If the value of `urlObject.hash` *does not start* with the ASCII hash (`#`)
character, the literal string `#` is appended to `result`.
* The value of `urlObject.hash` is appended to `result`.
* Otherwise, if the `urlObject.hash` property is not `undefined` and is not a
string, an [`Error`][] is thrown.
* `result` is returned.
### url.parse(urlString[, parseQueryString[, slashesDenoteHost]])
<!-- YAML
added: v0.1.25
-->
* `urlString` {string} The URL string to parse.
* `parseQueryString` {boolean} If `true`, the `query` property will always
be set to an object returned by the [`querystring`][] module's `parse()`
method. If `false`, the `query` property on the returned URL object will be an
unparsed, undecoded string. Defaults to `false`.
* `slashesDenoteHost` {boolean} If `true`, the first token after the literal
string `//` and preceding the next `/` will be interpreted as the `host`.
For instance, given `//foo/bar`, the result would be
`{host: 'foo', pathname: '/bar'}` rather than `{pathname: '//foo/bar'}`.
Defaults to `false`.
The `url.parse()` method takes a URL string, parses it, and returns a URL
object.
A `TypeError` is thrown if `urlString` is not a string.
A `URIError` is thrown if the `auth` property is present but cannot be decoded.
### url.resolve(from, to)
<!-- YAML
added: v0.1.25
changes:
- version: v6.6.0
pr-url: https://github.com/nodejs/node/pull/8215
description: The `auth` fields are now kept intact when `from` and `to`
refer to the same host.
- version: v6.5.0, v4.6.2
pr-url: https://github.com/nodejs/node/pull/8214
description: The `port` field is copied correctly now.
- version: v6.0.0
pr-url: https://github.com/nodejs/node/pull/1480
description: The `auth` fields is cleared now the `to` parameter
contains a hostname.
-->
* `from` {string} The Base URL being resolved against.
* `to` {string} The HREF URL being resolved.
The `url.resolve()` method resolves a target URL relative to a base URL in a
manner similar to that of a Web browser resolving an anchor tag HREF.
For example:
```js
url.resolve('/one/two/three', 'four'); // '/one/two/four'
url.resolve('http://example.com/', '/one'); // 'http://example.com/one'
url.resolve('http://example.com/one', '/two'); // 'http://example.com/two'
```
<a id="whatwg-percent-encoding"></a>
### Percent-Encoding in the WHATWG URL Standard
## Percent-Encoding in URLs
URLs are permitted to only contain a certain range of characters. Any character
falling outside of that range must be encoded. How such characters are encoded,
and which characters to encode depends entirely on where the character is
located within the structure of the URL. The WHATWG URL Standard uses a more
selective and fine grained approach to selecting encoded characters than that
used by the older [`url.parse()`][] and [`url.format()`][] methods.
located within the structure of the URL.
### Legacy API
Within the Legacy API, spaces (`' '`) and the following characters will be
automatically escaped in the properties of URL objects:
```txt
< > " ` \r \n \t { } | \ ^ '
```
For example, the ASCII space character (`' '`) is encoded as `%20`. The ASCII
forward slash (`/`) character is encoded as `%3C`.
### WHATWG API
The [WHATWG URL Standard][] uses a more selective and fine grained approach to
selecting encoded characters than that used by the Legacy API.
The WHATWG algorithm defines three "percent-encode sets" that describe ranges
of characters that must be percent-encoded:
@ -1101,7 +1104,6 @@ console.log(myURL.origin);
// Prints https://π.com
```
[`Error`]: errors.html#errors_class_error
[`JSON.stringify()`]: https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/JSON/stringify
[`Map`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map