regexr

Easily compose regular expressions. Doing this with strings would otherwise be tedious due to having to double-escape things.

Basic example:

const r = require('regexr')
const int = /\d+/
const USD = r`\$${int}(\.${int})?` // f.e. $3.45 or $5

(Note that int is an instance of RegExp and can be composed into the template string, and the resulting USD is also a RegExp)

Regexr provides an ES6 template tag function that makes it easy to compose RegExps using template strings without double-escaped hell.

In ES5 and below, we may try to compose the regular expressions like so:

const int = '\d+'
let USD = new RegExp('\$'+int+'(\.'+int+')?`) // this won't work!

but if you're experienced enough, you'd know that if you want to compose regular expressions using ES5 strings you have to escape the escape:

const int = '\\d+'
const USD = new RegExp('\\$'+int+'(\\.'+int+')?`) // correct!

Imagine making more complex regexes! For example, compare the following two examples achieving the same thing in ES5 and ES6 respectively:

// in ES5, the double escaping can get confusing:
var spaceRegex = '\\s*'
var finalRegex = '\\('+spaceRegex+'\\/\\[\\\\\\d+\\]\\)*$'
finalRegex = new RegExp(finalRegex, 'g')
console.log( !!'( /[\\12358])'.match(finalRegex) ) // true

// in ES6, we don't have to double escape, thanks to regexr:
var r = require('regexr')
var spaceRegex = r`\s*`
var finalRegex = r`/\(${spaceRegex}\/\[\\\d+\]\)*$/g`
console.log( !!'( /[\\12358])'.match(finalRegex) ) // true

API

r``

const r = require('regexr')

r`` is a template tag function that converts the given string into a RegExp without requiring double escaping. Instances of RegExp can be mixed into the string, and will be composed into the final RegExp.

Example:

const digit = /\d/
const integer = r`/${digit}+/`
const number = r`/${integer}|${digit}*\.${integer}|${integer}\.${digit}*/` // f.e. 4.2, .5, 5.

Hand-picked Regexes

Regexr comes with some pre-selected regular expressions. For example, we can rewrite the first example:

const r = require('regexr')
const USD = r`\$${r.integer}(\.${r.integer})?` // f.e. $3.45 or $5

where r.integer is an instance of RegExp.

r.identifier

Matches a valid JavaScript identifier. See this for details.

r.digit

Matches a single numerical digit (0-9).

Example:

!!" 8 ".match(r` ${r.digit} `) // true
!!" 25 ".match(r` ${r.digit} `) // false

r.integer

Matches 1 or more digits.

Example:

!!" 432 ".match(r` ${r.integer} `) // true

r.number

Matches a JavaScript Number.

Example:

!!"3".match(r.number) // true
!!"432".match(r.number) // true
!!"4.2".match(r.number) // true
!!"5.".match(r.number) // true
!!".34".match(r.number) // true