path-to-regexp

What is path-to-regexp?

The path-to-regexp package is a utility for converting paths to and from regular expressions. It is commonly used for routing in web applications, allowing developers to define patterns for URL paths and extract parameters from them.

What are path-to-regexp's main functionalities?

Path to RegExp Conversion

Convert a path string into a regular expression. It can also extract named parameter keys.

const { pathToRegexp } = require('path-to-regexp');
const keys = [];
const regexp = pathToRegexp('/user/:id', keys);

Extracting Parameters from a Path

Match a path against a pattern and extract the named parameters.

const { match } = require('path-to-regexp');
const matchFn = match('/user/:id');
const result = matchFn('/user/123');
// result.params will contain the extracted parameters

Compile Path to String

Compile a path function from a string pattern, which can then be used to construct paths with parameters.

const { compile } = require('path-to-regexp');
const toPath = compile('/user/:id');
const path = toPath({ id: 123 });
// path will be '/user/123'

Other packages similar to path-to-regexp

express

Express is a web application framework for Node.js that includes its own routing capabilities, which are similar to path-to-regexp. Express uses path-to-regexp internally for its routing logic.

react-router

React Router is a routing library for React that uses path-to-regexp-like pattern matching for defining routes and extracting parameters, but it is specifically tailored for React applications.

url-pattern

url-pattern is another library for matching URLs against patterns and extracting parameters. It offers a similar API to path-to-regexp but with different syntax and additional options for pattern matching.

README

Path-to-RegExp

Turn an Express-style path string such as /user/:name into a regular expression.

Installation

npm install path-to-regexp --save

Usage

var pathToRegexp = require('path-to-regexp')

// pathToRegexp(path, keys, options)
// pathToRegexp.parse(path)
// pathToRegexp.compile(path)

• path An Express-style string, an array of strings, or a regular expression.
• keys An array to be populated with the keys found in the path.
• options
  • sensitive When true the route will be case sensitive. (default: false)
  • strict When false the trailing slash is optional. (default: false)
  • end When false the path will match at the beginning. (default: true)

var keys = []
var re = pathToRegexp('/foo/:bar', keys)
// re = /^\/foo\/([^\/]+?)\/?$/i
// keys = [{ name: 'bar', prefix: '/', delimiter: '/', optional: false, repeat: false, pattern: '[^\\/]+?' }]

Parameters

The path string can be used to define parameters and populate the keys.

Named Parameters

Named parameters are defined by prefixing a colon to the parameter name (:foo). By default, the parameter will match until the following path segment.

var re = pathToRegexp('/:foo/:bar', keys)
// keys = [{ name: 'foo', prefix: '/', ... }, { name: 'bar', prefix: '/', ... }]

re.exec('/test/route')
//=> ['/test/route', 'test', 'route']

Please note: Named parameters must be made up of "word characters" ([A-Za-z0-9_]).

Path segments are defined by "prefix" characters (. or /). If a prefix is used, and the parameter is followed by the same prefix character or end of the path, it is considered a segment and the prefix is part of the match. This behavior is apparent when using optional parameters.

var re = pathToRegexp('/:prefix(apple-)?icon-:res(\\d+).png', keys)
// keys = [{ name: 'prefix', prefix: '', ... }, { name: 'res', prefix: '', ... }]

re.exec('/icon-76.png')
//=> ['/icon-76.png', undefined, '76']

Modified Parameters

Optional

Parameters can be suffixed with a question mark (?) to make the parameter optional. This will also make the prefix optional.

var re = pathToRegexp('/:foo/:bar?', keys)
// keys = [{ name: 'foo', ... }, { name: 'bar', delimiter: '/', optional: true, repeat: false }]

re.exec('/test')
//=> ['/test', 'test', undefined]

re.exec('/test/route')
//=> ['/test', 'test', 'route']

Zero or more

Parameters can be suffixed with an asterisk (*) to denote a zero or more parameter matches. The prefix is taken into account for each match.

var re = pathToRegexp('/:foo*', keys)
// keys = [{ name: 'foo', delimiter: '/', optional: true, repeat: true }]

re.exec('/')
//=> ['/', undefined]

re.exec('/bar/baz')
//=> ['/bar/baz', 'bar/baz']

One or more

Parameters can be suffixed with a plus sign (+) to denote a one or more parameter matches. The prefix is taken into account for each match.

var re = pathToRegexp('/:foo+', keys)
// keys = [{ name: 'foo', delimiter: '/', optional: false, repeat: true }]

re.exec('/')
//=> null

re.exec('/bar/baz')
//=> ['/bar/baz', 'bar/baz']

Custom Match Parameters

All parameters can be provided a custom regexp, which overrides the default ([^\/]+).

var re = pathToRegexp('/:foo(\\d+)', keys)
// keys = [{ name: 'foo', ... }]

re.exec('/123')
//=> ['/123', '123']

re.exec('/abc')
//=> null

Please note: Backslashes need to be escaped with another backslash in strings.

Unnamed Parameters

It is possible to write an unnamed parameter that only consists of a matching group. It works the same as a named parameter, except it will be numerically indexed.

var re = pathToRegexp('/:foo/(.*)', keys)
// keys = [{ name: 'foo', ... }, { name: 0, ... }]

re.exec('/test/route')
//=> ['/test/route', 'test', 'route']

Asterisk

An asterisk can be used for matching everything. It is equivalent to an unnamed matching group of (.*).

var re = pathToRegexp('/foo/*', keys)
// keys = [{ name: '0', ... }]

re.exec('/foo/bar/baz')
//=> ['/foo/bar/baz', 'bar/baz']

Parse

The parse function is exposed via pathToRegexp.parse. This will return an array of strings and keys.

var tokens = pathToRegexp.parse('/route/:foo/(.*)')

console.log(tokens[0])
//=> "/route"

console.log(tokens[1])
//=> { name: 'foo', prefix: '/', delimiter: '/', optional: false, repeat: false, pattern: '[^\\/]+?' }

console.log(tokens[2])
//=> { name: 0, prefix: '/', delimiter: '/', optional: false, repeat: false, pattern: '.*' }

Note: This method only works with Express-style strings.

Compile ("Reverse" Path-To-RegExp)

Path-To-RegExp exposes a compile function for transforming an Express-style path into a valid path.

var toPath = pathToRegexp.compile('/user/:id')

toPath({ id: 123 }) //=> "/user/123"
toPath({ id: 'café' }) //=> "/user/caf%C3%A9"
toPath({ id: '/' }) //=> "/user/%2F"

toPath({ id: ':' }) //=> "/user/%3A"
toPath({ id: ':' }, { pretty: true }) //=> "/user/:"

var toPathRepeated = pathToRegexp.compile('/:segment+')

toPathRepeated({ segment: 'foo' }) //=> "/foo"
toPathRepeated({ segment: ['a', 'b', 'c'] }) //=> "/a/b/c"

var toPathRegexp = pathToRegexp.compile('/user/:id(\\d+)')

toPathRegexp({ id: 123 }) //=> "/user/123"
toPathRegexp({ id: '123' }) //=> "/user/123"
toPathRegexp({ id: 'abc' }) //=> Throws `TypeError`.

Note: The generated function will throw on invalid input. It will do all necessary checks to ensure the generated path is valid. This method only works with strings.

Working with Tokens

Path-To-RegExp exposes the two functions used internally that accept an array of tokens.

• pathToRegexp.tokensToRegExp(tokens, options) Transform an array of tokens into a matching regular expression.
• pathToRegexp.tokensToFunction(tokens) Transform an array of tokens into a path generator function.

Compatibility with Express <= 4.x

Path-To-RegExp breaks compatibility with Express <= 4.x:

• No longer a direct conversion to a RegExp with sugar on top - it's a path matcher with named and unnamed matching groups
  • It's unlikely you previously abused this feature, it's rare and you could always use a RegExp instead
• All matching RegExp special characters can be used in a matching group. E.g. /:user(.*)
  • Other RegExp features are not support - no nested matching groups, non-capturing groups or look aheads
• Parameters have suffixes that augment meaning - *, + and ?. E.g. /:user*

TypeScript

Includes a .d.ts file for TypeScript users.

Live Demo

You can see a live demo of this library in use at express-route-tester.

License

MIT