URLPattern polyfills

URLPattern is a new web API for matching URLs. Its intended to both provide a convenient API for web developers and to be usable in other web APIs that need to match URLs; e.g. service workers. The explainer discusses the motivating use cases. There is also a design document that goes into more details.

This is a polyfill for the URLPattern and URLPatternList API currently in development in Chromium based browsers. A specification has not been written yet, but this follows the C++ implementation as well as possible and incorporates and passes the same test suite.

Once the initial Chromium prototype is complete we will gather feedback and iterate. When we believe the API is stable, we will then codify it in a spec.

Basic example

let p = new URLPattern({ pathname: '/foo/:name' });

let r = p.exec('https://example.com/foo/bar');
console.log(r.pathname.input); // "/foo/bar"
console.log(r.pathname.groups.name); // "bar"

let r2 = p.exec({ pathname: '/foo/baz' });
console.log(r2.pathname.groups.name); // "baz"

Example of matching same-origin JPG or PNG requests

// Match same-origin jpg or png URLs.
// Note: This uses a named group to make it easier to access
//       the result later.
const p = new URLPattern({
  pathname: '/*.:filetype(jpg|png)',
  baseURL: self.location
});

for (let url in url_list) {
  const r = p.exec(url);

  // skip non-matches
  if (!r) {
    continue;
  }

  if (r.pathname.groups['filetype'] === 'jpg') {
    // process jpg
  } else if (r.pathname.groups['filetype'] === 'png') {
    // process png
  }
}

The pattern in this case can be made simpler without the origin check by leaving off the baseURL.

// Match any URL ending with 'jpg' or 'png'.
const p = new URLPattern({ pathname: '/*.:filetype(jpg|png)' });

Example of Short Form Support

We are planning to also support a "short form" for initializing URLPattern objects. This is supported by the polyfill but not yet by the Chromium implementation.

For example:

const p = new URLPattern("https://*.example.com/foo/*");

Or:

const p = new URLPattern("foo/*", self.location);

API reference

API overview with typeScript type annotations is found below. Associated browser Web IDL can be found here.

class URLPattern {
  constructor(init: URLPatternInit);
  constructor(shortPattern: string, baseURL: string = ""));

  test(input: URLPattern | string): boolean;
  exec(input: URLPattern | string): URLPatternResult;
};

interface URLPatternInit {
  baseURL?: string;
  username?: string;
  password?: string;
  protocol?: string;
  hostname?: string;
  port?: string;
  pathname?: string;
  search?: string;
  hash?: string;
}

interface URLPatternComponentResult {
  input: string;
  groups: { [key: string]: string };
}

interface URLPatternResult {
  input: URLPatternInit | string;

  protocol: URLPatternComponentResult;
  username: URLPatternComponentResult;
  password: URLPatternComponentResult;
  hostname: URLPatternComponentResult;
  port: URLPatternComponentResult;
  pathname: URLPatternComponentResult;
  search: URLPatternComponentResult;
  hash: URLPatternComponentResult;
}

Pattern syntax

The pattern syntax here is based on what is used in the popular path-to-regexp library.

• An understanding of a "divider" that separates segments of the string. For the pathname this is typically the "/" character.
• A regex group defined by an enclosed set of parentheses. Inside of the parentheses a general regex may be defined.
• A named group that matches characters until the next divider. The named group begins with a ":" character and then a name. For example, "/:foo/:bar" has two named groups.
• A custom regex for a named group. In this case a set of parentheses with a regex immediately follows the named group; e.g. "/:foo(.*)" will override the default of matching to the next divider.
• A modifier may optionally follow a regex or named group. A modifier is a "?", "*", or "+" functions just as they do in regular expressions. When a group is optional or repeated and it's preceded by a divider then the divider is also optional or repeated. For example, "/foo/:bar?" will match "/foo", "/foo/", or "/foo/baz". Escaping the divider will make it required instead.
• A way to greedily match characters, even across dividers, by using "(.*)" (so-called unnamed groups).

Currently we plan to have these known differences with path-to-regexp:

• No support for custom prefixes and suffixes.

Canonicalization

URLs have a canonical form that is based on ASCII, meaning that internationalized domain names (hostnames) also have a canonical ASCII based representation, and that other components such as hash, search and pathname are encoded using percent encoding.

Currently URLPattern does not perform any encoding or normalization of the patterns. So a developer would need to URL encode unicode characters before passing the pattern into the constructor. Similarly, the constructor does not do things like flattening pathnames such as /foo/../bar to /bar. Currently the pattern must be written to target canonical URL output manually.

It does, however, perform these operations for test() and exec() input.

Encoding components can easily be done manually, but do not encoding the pattern syntax:

encodeURIComponent("?q=æøå")
// "%3Fq%3D%C3%A6%C3%B8%C3%A5"

new URL("https://ølerlækkernårdetermit.dk").hostname
// "xn--lerlkkernrdetermit-dubo78a.dk"

Learn more

• Explainer
• Design Document

Reporting a security issue

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