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A tiny (308B) utility that converts route patterns into RegExp. Limited alternative to `path-to-regexp` πŸ™‡β€β™‚οΈ
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A tiny (308B) utility that converts route patterns into RegExp. Limited alternative to path-to-regexp πŸ™‡

With regexparam, you may turn a pathing string (eg, /users/:id) into a regular expression.

An object with shape of { keys, pattern } is returned, where pattern is the RegExp and keys is an array of your parameter name(s) in the order that they appeared.

Unlike path-to-regexp, this module does not create a keys dictionary, nor mutate an existing variable. Also, this only ships a parser, which only accept strings. Similarly, and most importantly, regexparam only handles basic pathing operators:

  • Static (/foo, /foo/bar)
  • Parameter (/:title, /books/:title, /books/:genre/:title)
  • Parameter w/ Suffix (/movies/:title.mp4, /movies/:title.(mp4|mov))
  • Optional Parameters (/:title?, /books/:title?, /books/:genre/:title?)
  • Wildcards (*, /books/*, /books/:genre/*)

This module exposes two module definitions:

  • CommonJS: dist/regexparam.js
  • ESModule: dist/regexparam.mjs


$ npm install --save regexparam


const regexparam = require('regexparam');

// Example param-assignment
function exec(path, result) {
  let i=0, out={};
  let matches = result.pattern.exec(path);
  while (i < result.keys.length) {
    out[ result.keys[i] ] = matches[++i] || null;
  return out;

// Parameter, with Optional Parameter
// ---
let foo = regexparam('/books/:genre/:title?')
// foo.pattern => /^\/books\/([^\/]+?)(?:\/([^\/]+?))?\/?$/i
// foo.keys => ['genre', 'title']

foo.pattern.test('/books/horror'); //=> true
foo.pattern.test('/books/horror/goosebumps'); //=> true

exec('/books/horror', foo);
//=> { genre: 'horror', title: null }

exec('/books/horror/goosebumps', foo);
//=> { genre: 'horror', title: 'goosebumps' }

// Parameter, with suffix
// ---
let bar = regexparam('/movies/:title.(mp4|mov)');
// bar.pattern => /^\/movies\/([^\/]+?)\.(mp4|mov)\/?$/i
// bar.keys => ['title']

bar.pattern.test('/movies/narnia'); //=> false
bar.pattern.test('/movies/narnia.mp3'); //=> false
bar.pattern.test('/movies/narnia.mp4'); //=> true

exec('/movies/narnia.mp4', bar);
//=> { title: 'narnia' }

// Wildcard
// ---
let baz = regexparam('users/*');
// baz.pattern => /^\/users\/(.*)\/?$/i
// baz.keys => ['wild']

baz.pattern.test('/users'); //=> false
baz.pattern.test('/users/lukeed'); //=> true

exec('/users/lukeed/repos/new', baz);
//=> { wild: 'lukeed/repos/new' }

Important: When matching/testing against a generated RegExp, your path must begin with a leading slash ("/")!

Regular Expressions

For fine-tuned control, you may pass a RegExp value directly to regexparam as its only parameter.

In these situations, regexparam does not parse nor manipulate your pattern in any way! Because of this, regexparam has no "insight" on your route, and instead trusts your input fully. In code, this means that the return value's keys is always equal to false and the pattern is identical to your input value.

This also means that you must manage and parse your own keys~!
You may use named capture groups or traverse the matched segments manually the "old-fashioned" way:

Important: Please check your target browsers' and target Node.js runtimes' support!

// Named capture group
const named = regexparam(/^\/posts[/](?<year>[0-9]{4})[/](?<month>[0-9]{2})[/](?<title>[^\/]+)/i);
const { groups } = named.pattern.exec('/posts/2019/05/hello-world');
//=> { year: '2019', month: '05', title: 'hello-world' }

// Widely supported / "Old-fashioned"
const named = regexparam(/^\/posts[/]([0-9]{4})[/]([0-9]{2})[/]([^\/]+)/i);
const [url, year, month, title] = named.pattern.exec('/posts/2019/05/hello-world');
console.log(year, month, title);
//=> 2019 05 hello-world


There are two API variants:

  1. When passing a String input, the loose parameter is able to affect the output. View API

  2. When passing a RegExp value, that must be regexparam's only argument.
    Your pattern is saved as written, so loose is ignored entirely. View API

regexparam(str, loose)

Returns: Object

Returns a { keys, pattern } object, where pattern is a generated RegExp instance and keys is a list of extracted parameter names.


Type: String

The route/pathing string to convert.

Note: It does not matter if your str begins with a / β€” it will be added if missing.


Type: Boolean
Default: false

Should the RegExp match URLs that are longer than the str pattern itself?
By default, the generated RegExp will test that the URL begins and ends with the pattern.

const rgx = require('regexparam');

rgx('/users').pattern.test('/users/lukeed'); //=> false
rgx('/users', true).pattern.test('/users/lukeed'); //=> true

rgx('/users/:name').pattern.test('/users/lukeed/repos'); //=> false
rgx('/users/:name', true).pattern.test('/users/lukeed/repos'); //=> true


Returns: Object

Returns a { keys, pattern } object, where pattern is identical to your rgx and keys is false, always.


Type: RegExp

Your RegExp pattern.

Important: This pattern is used as is! No parsing or interpreting is done on your behalf.


  • trouter - A server-side HTTP router that extends from this module.
  • matchit - Similar (650B) library, but relies on String comparison instead of RegExps.


MIT Β© Luke Edwards

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