URL: URL() constructor

Note: This feature is available in Web Workers.

The URL() constructor returns a newly created URL object representing the URL defined by the parameters.

If the given base URL or the resulting URL are not valid URLs, the JavaScript TypeError exception is thrown.


new URL(url)
new URL(url, base)



A string or any other object with a stringifier — including, for example, an <a> or <area> element — that represents an absolute or relative URL. If url is a relative URL, base is required, and will be used as the base URL. If url is an absolute URL, a given base will be ignored.

base Optional

A string representing the base URL to use in cases where url is a relative URL. If not specified, it defaults to undefined.

Note: The url and base arguments will each be stringified from whatever value you pass, just like with other Web APIs that accept a string. In particular, you can use an existing URL object for either argument, and it will stringify to the object's href property.

The resulting URL is not simply a concatenation of url and base. The path sections of both arguments are merged according to RFC 3986 - Relative Resolution. Therefore a trailing slash in base or a leading slash in url affect how the resulting path is constructed. If you need a strict concatenation of the two arguments the url must not have a leading slash and the base must have a trailing slash. See the examples under Examples - Merging of url and base paths.


Exception Explanation
TypeError url (in the case of absolute URLs) or base + url (in the case of relative URLs) is not a valid URL.


// Base URLs:
let baseUrl = "https://developer.mozilla.org";

let A = new URL("/", baseUrl);
// => 'https://developer.mozilla.org/'

let B = new URL(baseUrl);
// => 'https://developer.mozilla.org/'

new URL("en-US/docs", B);
// => 'https://developer.mozilla.org/en-US/docs'

let D = new URL("/en-US/docs", B);
// => 'https://developer.mozilla.org/en-US/docs'

new URL("/en-US/docs", D);
// => 'https://developer.mozilla.org/en-US/docs'

new URL("/en-US/docs", A);
// => 'https://developer.mozilla.org/en-US/docs'

new URL("/en-US/docs", "https://developer.mozilla.org/fr-FR/toto");
// => 'https://developer.mozilla.org/en-US/docs'

// Invalid URLs:

new URL("/en-US/docs", "");
// Raises a TypeError exception as '' is not a valid URL

new URL("/en-US/docs");
// Raises a TypeError exception as '/en-US/docs' is not a valid URL

// Other cases:

new URL("http://www.example.com");
// => 'http://www.example.com/'

new URL("http://www.example.com", B);
// => 'http://www.example.com/'

new URL("", "https://example.com/?query=1");
// => 'https://example.com/?query=1' (Edge before 79 removes query arguments)

new URL("/a", "https://example.com/?query=1");
// => 'https://example.com/a' (see relative URLs)

new URL("//foo.com", "https://example.com");
// => 'https://foo.com/' (see relative URLs)

Merging of url and base paths

/* base path without trailing slash */

const A = new URL("articles", "https://developer.mozilla.org/api/v1");
// => 'https://developer.mozilla.org/api/articles'

const B = new URL("/articles", "https://developer.mozilla.org/api/v1");
// => 'https://developer.mozilla.org/articles'

const C = new URL("./articles", "https://developer.mozilla.org/api/v1");
// => 'https://developer.mozilla.org/api/articles'

const D = new URL("../articles", "https://developer.mozilla.org/api/v1");
// => 'https://developer.mozilla.org/articles'

/* base path with trailing slash */

const E = new URL("articles", "https://developer.mozilla.org/api/v1/");
// => 'https://developer.mozilla.org/api/v1/articles'

const F = new URL("/articles", "https://developer.mozilla.org/api/v1/");
// => 'https://developer.mozilla.org/articles'

const G = new URL("./articles", "https://developer.mozilla.org/api/v1/");
// => 'https://developer.mozilla.org/api/v1/articles'

const H = new URL("../articles", "https://developer.mozilla.org/api/v1/");
// => 'https://developer.mozilla.org/api/articles'


URL Standard
# dom-url-url

Browser compatibility

BCD tables only load in the browser

See also