# regexparam [](https://travis-ci.org/lukeed/regexparam)
> A tiny (308B) utility that converts route patterns into RegExp. Limited alternative to [`path-to-regexp`](https://github.com/pillarjs/path-to-regexp) 🙇
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`](https://github.com/pillarjs/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`
## Install
```
$ npm install --save regexparam
```
## Usage
```js
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](https://javascript.info/regexp-groups#named-groups) or traverse the matched segments manually the "old-fashioned" way:
> **Important:** Please check your target browsers' and target [Node.js runtimes' support](https://node.green/#ES2018-features--RegExp-named-capture-groups)!
```js
// Named capture group
const named = regexparam(/^\/posts[/](?[0-9]{4})[/](?[0-9]{2})[/](?[^\/]+)/i);
const { groups } = named.pattern.exec('/posts/2019/05/hello-world');
console.log(groups);
//=> { 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
```
## API
There are two API variants:
1) When passing a `String` input, the `loose` parameter is able to affect the output. [View API](#regexparamstr-loose)
2) When passing a `RegExp` value, that must be `regexparam`'s _only_ argument.<br>
Your pattern is saved as written, so `loose` is ignored entirely. [View API](#regexparamrgx)
### 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.
#### str
Type: `String`
The route/pathing string to convert.
> **Note:** It does not matter if your `str` begins with a `/` — it will be added if missing.
#### loose
Type: `Boolean`<br>
Default: `false`
Should the `RegExp` match URLs that are longer than the [`str`](#str) pattern itself?<br>
By default, the generated `RegExp` will test that the URL begins and _ends with_ the pattern.
```js
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
```
### regexparam(rgx)
Returns: `Object`
Returns a `{ keys, pattern }` object, where pattern is _identical_ to your `rgx` and `keys` is `false`, always.
#### rgx
Type: `RegExp`
Your RegExp pattern.
> **Important:** This pattern is used _as is_! No parsing or interpreting is done on your behalf.
## Related
- [trouter](https://github.com/lukeed/trouter) - A server-side HTTP router that extends from this module.
- [matchit](https://github.com/lukeed/matchit) - Similar (650B) library, but relies on String comparison instead of `RegExp`s.
## License
MIT © [Luke Edwards](https://lukeed.com)