UNB/ CS/ David Bremner/ teaching/ cs2613/ books/ nodejs-api/ url

URL

Stability: 2 - Stable

The url module provides utilities for URL resolution and parsing. It can be accessed using:

const url = require('url');

URL strings and URL objects

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 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.

A comparison between the WHATWG and Legacy APIs is provided below. Above the URL 'http://user:pass@sub.example.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.

WHATWG URL's origin property includes protocol and host, but not username or password.

┌────────────────────────────────────────────────────────────────────────────────────────────────┐
│                                              href                                              │
├──────────┬──┬─────────────────────┬────────────────────────┬───────────────────────────┬───────┤
│ protocol │  │        auth         │          host          │           path            │ hash  │
│          │  │                     ├─────────────────┬──────┼──────────┬────────────────┤       │
│          │  │                     │    hostname     │ port │ pathname │     search     │       │
│          │  │                     │                 │      │          ├─┬──────────────┤       │
│          │  │                     │                 │      │          │ │    query     │       │
"  https:   //    user   :   pass   @ sub.example.com : 8080   /p/a/t/h  ?  query=string   #hash "
│          │  │          │          │    hostname     │ port │          │                │       │
│          │  │          │          ├─────────────────┴──────┤          │                │       │
│ protocol │  │ username │ password │          host          │          │                │       │
├──────────┴──┼──────────┴──────────┼────────────────────────┤          │                │       │
│   origin    │                     │         origin         │ pathname │     search     │ hash  │
├─────────────┴─────────────────────┴────────────────────────┴──────────┴────────────────┴───────┤
│                                              href                                              │
└────────────────────────────────────────────────────────────────────────────────────────────────┘
(All spaces in the "" line should be ignored. They are purely for formatting.)

Parsing the URL string using the WHATWG API:

const myURL =
  new URL('https://user:pass@sub.example.com:8080/p/a/t/h?query=string#hash');

Parsing the URL string using the Legacy API:

const url = require('url');
const myURL =
  url.parse('https://user:pass@sub.example.com:8080/p/a/t/h?query=string#hash');

The WHATWG URL API

Class: URL

Browser-compatible URL class, implemented by following the WHATWG URL Standard. Examples of parsed URLs may be found in the Standard itself. The URL class is also available on the global object.

In accordance with browser conventions, all properties of URL objects are implemented as getters and setters on the class prototype, rather than as data properties on the object itself. Thus, unlike legacy urlObjects, using the delete keyword on any properties of URL objects (e.g. delete myURL.protocol, delete myURL.pathname, etc) has no effect but will still return true.

new URL(input[, base])

Creates a new URL object by parsing the input relative to the base. If base is passed as a string, it will be parsed equivalent to new URL(base).

const myURL = new URL('/foo', 'https://example.org/');
// https://example.org/foo

The URL constructor is accessible as a property on the global object. It can also be imported from the built-in url module:

console.log(URL === require('url').URL); // Prints 'true'.

A TypeError will be thrown if the input or base are not valid URLs. Note that an effort will be made to coerce the given values into strings. For instance:

const myURL = new URL({ toString: () => 'https://example.org/' });
// https://example.org/

Unicode characters appearing within the host name of input will be automatically converted to ASCII using the Punycode algorithm.

const myURL = new URL('https://測試');
// https://xn--g6w251d/

This feature is only available if the node executable was compiled with ICU enabled. If not, the domain names are passed through unchanged.

In cases where it is not known in advance if input is an absolute URL and a base is provided, it is advised to validate that the origin of the URL object is what is expected.

let myURL = new URL('http://Example.com/', 'https://example.org/');
// http://example.com/

myURL = new URL('https://Example.com/', 'https://example.org/');
// https://example.com/

myURL = new URL('foo://Example.com/', 'https://example.org/');
// foo://Example.com/

myURL = new URL('http:Example.com/', 'https://example.org/');
// http://example.com/

myURL = new URL('https:Example.com/', 'https://example.org/');
// https://example.org/Example.com/

myURL = new URL('foo:Example.com/', 'https://example.org/');
// foo:Example.com/

url.hash

Gets and sets the fragment portion of the URL.

const myURL = new URL('https://example.org/foo#bar');
console.log(myURL.hash);
// Prints #bar

myURL.hash = 'baz';
console.log(myURL.href);
// Prints https://example.org/foo#baz

Invalid URL characters included in the value assigned to the hash property are percent-encoded. The selection of which characters to percent-encode may vary somewhat from what the url.parse() and url.format() methods would produce.

url.host

Gets and sets the host portion of the URL.

const myURL = new URL('https://example.org:81/foo');
console.log(myURL.host);
// Prints example.org:81

myURL.host = 'example.com:82';
console.log(myURL.href);
// Prints https://example.com:82/foo

Invalid host values assigned to the host property are ignored.

url.hostname

Gets and sets the host name portion of the URL. The key difference between url.host and url.hostname is that url.hostname does not include the port.

const myURL = new URL('https://example.org:81/foo');
console.log(myURL.hostname);
// Prints example.org

myURL.hostname = 'example.com:82';
console.log(myURL.href);
// Prints https://example.com:81/foo

Invalid host name values assigned to the hostname property are ignored.

url.href

Gets and sets the serialized URL.

const myURL = new URL('https://example.org/foo');
console.log(myURL.href);
// Prints https://example.org/foo

myURL.href = 'https://example.com/bar';
console.log(myURL.href);
// Prints https://example.com/bar

Getting the value of the href property is equivalent to calling url.toString().

Setting the value of this property to a new value is equivalent to creating a new URL object using new URL(value). Each of the URL object's properties will be modified.

If the value assigned to the href property is not a valid URL, a TypeError will be thrown.

url.origin

Gets the read-only serialization of the URL's origin.

const myURL = new URL('https://example.org/foo/bar?baz');
console.log(myURL.origin);
// Prints https://example.org

const idnURL = new URL('https://測試');
console.log(idnURL.origin);
// Prints https://xn--g6w251d

console.log(idnURL.hostname);
// Prints xn--g6w251d

url.password

Gets and sets the password portion of the URL.

const myURL = new URL('https://abc:xyz@example.com');
console.log(myURL.password);
// Prints xyz

myURL.password = '123';
console.log(myURL.href);
// Prints https://abc:123@example.com

Invalid URL characters included in the value assigned to the password property are percent-encoded. The selection of which characters to percent-encode may vary somewhat from what the url.parse() and url.format() methods would produce.

url.pathname

Gets and sets the path portion of the URL.

const myURL = new URL('https://example.org/abc/xyz?123');
console.log(myURL.pathname);
// Prints /abc/xyz

myURL.pathname = '/abcdef';
console.log(myURL.href);
// Prints https://example.org/abcdef?123

Invalid URL characters included in the value assigned to the pathname property are percent-encoded. The selection of which characters to percent-encode may vary somewhat from what the url.parse() and url.format() methods would produce.

url.port

Gets and sets the port portion of the URL.

The port value may be a number or a string containing a number in the range 0 to 65535 (inclusive). Setting the value to the default port of the URL objects given protocol will result in the port value becoming the empty string ('').

The port value can be an empty string in which case the port depends on the protocol/scheme:

protocol port
"ftp" 21
"file"
"gopher" 70
"http" 80
"https" 443
"ws" 80
"wss" 443

Upon assigning a value to the port, the value will first be converted to a string using .toString().

If that string is invalid but it begins with a number, the leading number is assigned to port. If the number lies outside the range denoted above, it is ignored.

const myURL = new URL('https://example.org:8888');
console.log(myURL.port);
// Prints 8888

// Default ports are automatically transformed to the empty string
// (HTTPS protocol's default port is 443)
myURL.port = '443';
console.log(myURL.port);
// Prints the empty string
console.log(myURL.href);
// Prints https://example.org/

myURL.port = 1234;
console.log(myURL.port);
// Prints 1234
console.log(myURL.href);
// Prints https://example.org:1234/

// Completely invalid port strings are ignored
myURL.port = 'abcd';
console.log(myURL.port);
// Prints 1234

// Leading numbers are treated as a port number
myURL.port = '5678abcd';
console.log(myURL.port);
// Prints 5678

// Non-integers are truncated
myURL.port = 1234.5678;
console.log(myURL.port);
// Prints 1234

// Out-of-range numbers which are not represented in scientific notation
// will be ignored.
myURL.port = 1e10; // 10000000000, will be range-checked as described below
console.log(myURL.port);
// Prints 1234

Numbers which contain a decimal point, such as floating-point numbers or numbers in scientific notation, are not an exception to this rule. Leading numbers up to the decimal point will be set as the URL's port, assuming they are valid:

myURL.port = 4.567e21;
console.log(myURL.port);
// Prints 4 (because it is the leading number in the string '4.567e21')

url.protocol

Gets and sets the protocol portion of the URL.

const myURL = new URL('https://example.org');
console.log(myURL.protocol);
// Prints https:

myURL.protocol = 'ftp';
console.log(myURL.href);
// Prints ftp://example.org/

Invalid URL protocol values assigned to the protocol property are ignored.

Special schemes

The WHATWG URL Standard considers a handful of URL protocol schemes to be special in terms of how they are parsed and serialized. When a URL is parsed using one of these special protocols, the url.protocol property may be changed to another special protocol but cannot be changed to a non-special protocol, and vice versa.

For instance, changing from http to https works:

const u = new URL('http://example.org');
u.protocol = 'https';
console.log(u.href);
// https://example.org

However, changing from http to a hypothetical fish protocol does not because the new protocol is not special.

const u = new URL('http://example.org');
u.protocol = 'fish';
console.log(u.href);
// http://example.org

Likewise, changing from a non-special protocol to a special protocol is also not permitted:

const u = new URL('fish://example.org');
u.protocol = 'http';
console.log(u.href);
// fish://example.org

According to the WHATWG URL Standard, special protocol schemes are ftp, file, gopher, http, https, ws, and wss.

url.search

Gets and sets the serialized query portion of the URL.

const myURL = new URL('https://example.org/abc?123');
console.log(myURL.search);
// Prints ?123

myURL.search = 'abc=xyz';
console.log(myURL.href);
// Prints https://example.org/abc?abc=xyz

Any invalid URL characters appearing in the value assigned the search property will be percent-encoded. The selection of which characters to percent-encode may vary somewhat from what the url.parse() and url.format() methods would produce.

url.searchParams

Gets the URLSearchParams object representing the query parameters of the URL. This property is read-only but the URLSearchParams object it provides can be used to mutate the URL instance; to replace the entirety of query parameters of the URL, use the url.search setter. See URLSearchParams documentation for details.

Use care when using .searchParams to modify the URL because, per the WHATWG specification, the URLSearchParams object uses different rules to determine which characters to percent-encode. For instance, the URL object will not percent encode the ASCII tilde (~) character, while URLSearchParams will always encode it:

const myUrl = new URL('https://example.org/abc?foo=~bar');

console.log(myUrl.search);  // prints ?foo=~bar

// Modify the URL via searchParams...
myUrl.searchParams.sort();

console.log(myUrl.search);  // prints ?foo=%7Ebar

url.username

Gets and sets the username portion of the URL.

const myURL = new URL('https://abc:xyz@example.com');
console.log(myURL.username);
// Prints abc

myURL.username = '123';
console.log(myURL.href);
// Prints https://123:xyz@example.com/

Any invalid URL characters appearing in the value assigned the username property will be percent-encoded. The selection of which characters to percent-encode may vary somewhat from what the url.parse() and url.format() methods would produce.

url.toString()

The toString() method on the URL object returns the serialized URL. The value returned is equivalent to that of url.href and url.toJSON().

Because of the need for standard compliance, this method does not allow users to customize the serialization process of the URL. For more flexibility, require('url').format() method might be of interest.

url.toJSON()

The toJSON() method on the URL object returns the serialized URL. The value returned is equivalent to that of url.href and url.toString().

This method is automatically called when an URL object is serialized with JSON.stringify().

const myURLs = [
  new URL('https://www.example.com'),
  new URL('https://test.example.org')
];
console.log(JSON.stringify(myURLs));
// Prints ["https://www.example.com/","https://test.example.org/"]

Class: URLSearchParams

The URLSearchParams API provides read and write access to the query of a URL. The URLSearchParams class can also be used standalone with one of the four following constructors. The URLSearchParams class is also available on the global object.

The WHATWG URLSearchParams interface and the querystring module have similar purpose, but the purpose of the querystring module is more general, as it allows the customization of delimiter characters (& and =). On the other hand, this API is designed purely for URL query strings.

const myURL = new URL('https://example.org/?abc=123');
console.log(myURL.searchParams.get('abc'));
// Prints 123

myURL.searchParams.append('abc', 'xyz');
console.log(myURL.href);
// Prints https://example.org/?abc=123&abc=xyz

myURL.searchParams.delete('abc');
myURL.searchParams.set('a', 'b');
console.log(myURL.href);
// Prints https://example.org/?a=b

const newSearchParams = new URLSearchParams(myURL.searchParams);
// The above is equivalent to
// const newSearchParams = new URLSearchParams(myURL.search);

newSearchParams.append('a', 'c');
console.log(myURL.href);
// Prints https://example.org/?a=b
console.log(newSearchParams.toString());
// Prints a=b&a=c

// newSearchParams.toString() is implicitly called
myURL.search = newSearchParams;
console.log(myURL.href);
// Prints https://example.org/?a=b&a=c
newSearchParams.delete('a');
console.log(myURL.href);
// Prints https://example.org/?a=b&a=c

new URLSearchParams()

Instantiate a new empty URLSearchParams object.

new URLSearchParams(string)

Parse the string as a query string, and use it to instantiate a new URLSearchParams object. A leading '?', if present, is ignored.

let params;

params = new URLSearchParams('user=abc&query=xyz');
console.log(params.get('user'));
// Prints 'abc'
console.log(params.toString());
// Prints 'user=abc&query=xyz'

params = new URLSearchParams('?user=abc&query=xyz');
console.log(params.toString());
// Prints 'user=abc&query=xyz'

new URLSearchParams(obj)

Instantiate a new URLSearchParams object with a query hash map. The key and value of each property of obj are always coerced to strings.

Unlike querystring module, duplicate keys in the form of array values are not allowed. Arrays are stringified using array.toString(), which simply joins all array elements with commas.

const params = new URLSearchParams({
  user: 'abc',
  query: ['first', 'second']
});
console.log(params.getAll('query'));
// Prints [ 'first,second' ]
console.log(params.toString());
// Prints 'user=abc&query=first%2Csecond'

new URLSearchParams(iterable)

Instantiate a new URLSearchParams object with an iterable map in a way that is similar to Map's constructor. iterable can be an Array or any iterable object. That means iterable can be another URLSearchParams, in which case the constructor will simply create a clone of the provided URLSearchParams. Elements of iterable are key-value pairs, and can themselves be any iterable object.

Duplicate keys are allowed.

let params;

// Using an array
params = new URLSearchParams([
  ['user', 'abc'],
  ['query', 'first'],
  ['query', 'second']
]);
console.log(params.toString());
// Prints 'user=abc&query=first&query=second'

// Using a Map object
const map = new Map();
map.set('user', 'abc');
map.set('query', 'xyz');
params = new URLSearchParams(map);
console.log(params.toString());
// Prints 'user=abc&query=xyz'

// Using a generator function
function* getQueryPairs() {
  yield ['user', 'abc'];
  yield ['query', 'first'];
  yield ['query', 'second'];
}
params = new URLSearchParams(getQueryPairs());
console.log(params.toString());
// Prints 'user=abc&query=first&query=second'

// Each key-value pair must have exactly two elements
new URLSearchParams([
  ['user', 'abc', 'error']
]);
// Throws TypeError [ERR_INVALID_TUPLE]:
//        Each query pair must be an iterable [name, value] tuple

urlSearchParams.append(name, value)

Append a new name-value pair to the query string.

urlSearchParams.delete(name)

Remove all name-value pairs whose name is name.

urlSearchParams.entries()

Returns an ES6 Iterator over each of the name-value pairs in the query. Each item of the iterator is a JavaScript Array. The first item of the Array is the name, the second item of the Array is the value.

Alias for urlSearchParams[@@iterator]().

urlSearchParams.forEach(fn[, thisArg])

Iterates over each name-value pair in the query and invokes the given function.

const myURL = new URL('https://example.org/?a=b&c=d');
myURL.searchParams.forEach((value, name, searchParams) => {
  console.log(name, value, myURL.searchParams === searchParams);
});
// Prints:
//   a b true
//   c d true

urlSearchParams.get(name)

Returns the value of the first name-value pair whose name is name. If there are no such pairs, null is returned.

urlSearchParams.getAll(name)

Returns the values of all name-value pairs whose name is name. If there are no such pairs, an empty array is returned.

urlSearchParams.has(name)

Returns true if there is at least one name-value pair whose name is name.

urlSearchParams.keys()

Returns an ES6 Iterator over the names of each name-value pair.

const params = new URLSearchParams('foo=bar&foo=baz');
for (const name of params.keys()) {
  console.log(name);
}
// Prints:
//   foo
//   foo

urlSearchParams.set(name, value)

Sets the value in the URLSearchParams object associated with name to value. If there are any pre-existing name-value pairs whose names are name, set the first such pair's value to value and remove all others. If not, append the name-value pair to the query string.

const params = new URLSearchParams();
params.append('foo', 'bar');
params.append('foo', 'baz');
params.append('abc', 'def');
console.log(params.toString());
// Prints foo=bar&foo=baz&abc=def

params.set('foo', 'def');
params.set('xyz', 'opq');
console.log(params.toString());
// Prints foo=def&abc=def&xyz=opq

urlSearchParams.sort()

Sort all existing name-value pairs in-place by their names. Sorting is done with a stable sorting algorithm, so relative order between name-value pairs with the same name is preserved.

This method can be used, in particular, to increase cache hits.

const params = new URLSearchParams('query[]=abc&type=search&query[]=123');
params.sort();
console.log(params.toString());
// Prints query%5B%5D=abc&query%5B%5D=123&type=search

urlSearchParams.toString()

Returns the search parameters serialized as a string, with characters percent-encoded where necessary.

urlSearchParams.values()

Returns an ES6 Iterator over the values of each name-value pair.

urlSearchParams[Symbol.iterator]()

Returns an ES6 Iterator over each of the name-value pairs in the query string. Each item of the iterator is a JavaScript Array. The first item of the Array is the name, the second item of the Array is the value.

Alias for urlSearchParams.entries().

const params = new URLSearchParams('foo=bar&xyz=baz');
for (const [name, value] of params) {
  console.log(name, value);
}
// Prints:
//   foo bar
//   xyz baz

url.domainToASCII(domain)

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().

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)

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().

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.fileURLToPath(url)

This function ensures the correct decodings of percent-encoded characters as well as ensuring a cross-platform valid absolute path string.

new URL('file:///C:/path/').pathname;    // Incorrect: /C:/path/
fileURLToPath('file:///C:/path/');       // Correct:   C:\path\ (Windows)

new URL('file://nas/foo.txt').pathname;  // Incorrect: /foo.txt
fileURLToPath('file://nas/foo.txt');     // Correct:   \\nas\foo.txt (Windows)

new URL('file:///你好.txt').pathname;    // Incorrect: /%E4%BD%A0%E5%A5%BD.txt
fileURLToPath('file:///你好.txt');       // Correct:   /你好.txt (POSIX)

new URL('file:///hello world').pathname; // Incorrect: /hello%20world
fileURLToPath('file:///hello world');    // Correct:   /hello world (POSIX)

url.format(URL[, options])

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.

const myURL = new URL('https://a:b@測試?abc#foo');

console.log(myURL.href);
// Prints https://a:b@xn--g6w251d/?abc#foo

console.log(myURL.toString());
// Prints https://a:b@xn--g6w251d/?abc#foo

console.log(url.format(myURL, { fragment: false, unicode: true, auth: false }));
// Prints 'https://測試/?abc'

url.pathToFileURL(path)

This function ensures that path is resolved absolutely, and that the URL control characters are correctly encoded when converting into a File URL.

new URL(__filename);                // Incorrect: throws (POSIX)
new URL(__filename);                // Incorrect: C:\... (Windows)
pathToFileURL(__filename);          // Correct:   file:///... (POSIX)
pathToFileURL(__filename);          // Correct:   file:///C:/... (Windows)

new URL('/foo#1', 'file:');         // Incorrect: file:///foo#1
pathToFileURL('/foo#1');            // Correct:   file:///foo%231 (POSIX)

new URL('/some/path%.c', 'file:'); // Incorrect: file:///some/path%.c
pathToFileURL('/some/path%.c');    // Correct:   file:///some/path%25.c (POSIX)

Legacy URL API

Legacy urlObject

Stability: 0 - Deprecated: Use the WHATWG URL API instead.

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 @. The string is either the username, or it is the username and password separated by :.

For example: 'user:pass'.

urlObject.hash

The hash property is the fragment identifier portion of the URL including the leading # 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.example.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.example.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.example.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)

Stability: 0 - Deprecated: Use the WHATWG URL API instead.

The url.format() method returns a formatted URL string derived from urlObject.

url.format({
  protocol: 'https',
  hostname: 'example.com',
  pathname: '/some/path',
  query: {
    page: 1,
    format: 'json'
  }
});

// => 'https://example.com/some/path?page=1&format=json'

If urlObject is not an object or a string, url.format() will throw a TypeError.

The formatting process operates as follows:

url.parse(urlString[, parseQueryString[, slashesDenoteHost]])

Stability: 0 - Deprecated: Use the WHATWG URL API instead.

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.

Use of the legacy url.parse() method is discouraged. Users should use the WHATWG URL API. Because the url.parse() method uses a lenient, non-standard algorithm for parsing URL strings, security issues can be introduced. Specifically, issues with host name spoofing and incorrect handling of usernames and passwords have been identified.

url.resolve(from, to)

Stability: 0 - Deprecated: Use the WHATWG URL API instead.

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.

const url = require('url');
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'

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.

Legacy API

Within the Legacy API, spaces (' ') and the following characters will be automatically escaped in the properties of URL objects:

< > " ` \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 four "percent-encode sets" that describe ranges of characters that must be percent-encoded:

The userinfo percent-encode set is used exclusively for username and passwords encoded within the URL. The path percent-encode set is used for the path of most URLs. The fragment percent-encode set is used for URL fragments. The C0 control percent-encode set is used for host and path under certain specific conditions, in addition to all other cases.

When non-ASCII characters appear within a host name, the host name is encoded using the Punycode algorithm. Note, however, that a host name may contain both Punycode encoded and percent-encoded characters:

const myURL = new URL('https://%CF%80.example.com/foo');
console.log(myURL.href);
// Prints https://xn--1xa.example.com/foo
console.log(myURL.origin);
// Prints https://xn--1xa.example.com