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 a path string such as /user/:name into a regular expression.

Installation

npm install path-to-regexp --save

Usage

const {
  pathToRegexp,
  match,
  parse,
  compile,
  normalizePathname
} = require("path-to-regexp");

// pathToRegexp(path, keys?, options?)
// match(path)
// parse(path)
// compile(path)
// normalizePathname(path)

• path A string, array of strings, or a regular expression.
• keys An array to populate with keys found in the path.
• options
  • sensitive When true the regexp will be case sensitive. (default: false)
  • strict When true the regexp allows an optional trailing delimiter to match. (default: false)
  • end When true the regexp will match to the end of the string. (default: true)
  • start When true the regexp will match from the beginning of the string. (default: true)
  • delimiter The default delimiter for segments. (default: '/')
  • endsWith Optional character, or list of characters, to treat as "end" characters.
  • whitelist List of characters to consider delimiters when parsing. (default: undefined, any character)

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

Please note: The RegExp returned by path-to-regexp is intended for ordered data (e.g. pathnames, hostnames). It can not handle arbitrarily ordered data (e.g. query strings, URL fragments, JSON, etc).

Parameters

The path argument is used to define parameters and populate the list of keys.

Named Parameters

Named parameters are defined by prefixing a colon to the parameter name (:foo). By default, the parameter will match until the next prefix (e.g. [^/]+).

const regexp = pathToRegexp("/:foo/:bar");
// keys = [{ name: 'foo', prefix: '/', ... }, { name: 'bar', prefix: '/', ... }]

regexp.exec("/test/route");
//=> [ '/test/route', 'test', 'route', index: 0, input: '/test/route', groups: undefined ]

Please note: Parameter names must use "word characters" ([A-Za-z0-9_]).

Parameter Modifiers

Optional

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

const regexp = pathToRegexp("/:foo/:bar?");
// keys = [{ name: 'foo', ... }, { name: 'bar', delimiter: '/', optional: true, repeat: false }]

regexp.exec("/test");
//=> [ '/test', 'test', undefined, index: 0, input: '/test', groups: undefined ]

regexp.exec("/test/route");
//=> [ '/test/route', 'test', 'route', index: 0, input: '/test/route', groups: undefined ]

Tip: The prefix is also optional, escape the prefix \/ to make it required.

Zero or more

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

const regexp = pathToRegexp("/:foo*");
// keys = [{ name: 'foo', delimiter: '/', optional: true, repeat: true }]

regexp.exec("/");
//=> [ '/', undefined, index: 0, input: '/', groups: undefined ]

regexp.exec("/bar/baz");
//=> [ '/bar/baz', 'bar/baz', index: 0, input: '/bar/baz', groups: undefined ]

One or more

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

const regexp = pathToRegexp("/:foo+");
// keys = [{ name: 'foo', delimiter: '/', optional: false, repeat: true }]

regexp.exec("/");
//=> null

regexp.exec("/bar/baz");
//=> [ '/bar/baz','bar/baz', index: 0, input: '/bar/baz', groups: undefined ]

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.

const regexp = pathToRegexp("/:foo/(.*)");
// keys = [{ name: 'foo', ... }, { name: 0, ... }]

regexp.exec("/test/route");
//=> [ '/test/route', 'test', 'route', index: 0, input: '/test/route', groups: undefined ]

Custom Matching Parameters

All parameters can have a custom regexp, which overrides the default match ([^/]+). For example, you can match digits or names in a path:

const regexpNumbers = pathToRegexp("/icon-:foo(\\d+).png");
// keys = [{ name: 'foo', ... }]

regexpNumbers.exec("/icon-123.png");
//=> ['/icon-123.png', '123']

regexpNumbers.exec("/icon-abc.png");
//=> null

const regexpWord = pathToRegexp("/(user|u)");
// keys = [{ name: 0, ... }]

regexpWord.exec("/u");
//=> ['/u', 'u']

regexpWord.exec("/users");
//=> null

Tip: Backslashes need to be escaped with another backslash in JavaScript strings.

Match

The match function will return a function for transforming paths into parameters:

const match = match("/user/:id");

match("/user/123"); //=> { path: '/user/123', index: 0, params: { id: '123' } }
match("/invalid"); //=> false

Normalize Pathname

The normalizePathname function will return a normalized string for matching with pathToRegexp.

const re = pathToRegexp("/caf\u00E9");
const input = encodeURI("/cafe\u0301");

re.test(input); //=> false
re.test(normalizePathname(input)); //=> true

Parse

The parse function will return a list of strings and keys from a path string:

const tokens = 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 strings.

Compile ("Reverse" Path-To-RegExp)

The compile function will return a function for transforming parameters into a valid path:

const toPath = compile("/user/:id");

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

toPath({ id: ":/" }); //=> "/user/%3A%2F"
toPath({ id: ":/" }, { encode: (value, token) => value, validate: false }); //=> "/user/:/"

const toPathRepeated = compile("/:segment+");

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

const toPathRegexp = compile("/user/:id(\\d+)");

toPathRegexp({ id: 123 }); //=> "/user/123"
toPathRegexp({ id: "123" }); //=> "/user/123"
toPathRegexp({ id: "abc" }); //=> Throws `TypeError`.
toPathRegexp({ id: "abc" }, { validate: false }); //=> "/user/abc"

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.

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

Token Information

• name The name of the token (string for named or number for unnamed index)
• prefix The prefix character for the segment (e.g. /)
• delimiter The delimiter for the segment (same as prefix or default delimiter)
• optional Indicates the token is optional (boolean)
• repeat Indicates the token is repeated (boolean)
• pattern The RegExp used to match this token (string)

Compatibility with Express <= 4.x

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

• RegExp special characters can only be used in a parameter
  • Express.js 4.x supported RegExp special characters regardless of position - this is considered a bug
• Parameters have suffixes that augment meaning - *, + and ?. E.g. /:user*
• No wildcard asterisk (*) - use parameters instead ((.*) or :splat*)

Live Demo

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

License

MIT