This libary generates thesource string to be passed tonew RegExp() for matching a range of numbers.

Example

consttoRegexRange=require('to-regex-range');constregex=newRegExp(toRegexRange('15','95'));

A string is returned so that you can do whatever you need with it before passing it tonew RegExp() (like adding^ or$ boundaries, defining flags, or combining it another string).

Creating regular expressions for matching numbers gets deceptively complicated pretty fast.

For example, let's say you need a validation regex for matching part of a user-id, postal code, social security number, tax id, etc:

• regex for matching1 =>/1/ (easy enough)
• regex for matching1 through5 =>/[1-5]/ (not bad...)
• regex for matching1 or5 =>/(1|5)/ (still easy...)
• regex for matching1 through50 =>/([1-9]|[1-4][0-9]|50)/ (uh-oh...)
• regex for matching1 through55 =>/([1-9]|[1-4][0-9]|5[0-5])/ (no prob, I can do this...)
• regex for matching1 through555 =>/([1-9]|[1-9][0-9]|[1-4][0-9]{2}|5[0-4][0-9]|55[0-5])/ (maybe not...)
• regex for matching0001 through5555 =>/(0{3}[1-9]|0{2}[1-9][0-9]|0[1-9][0-9]{2}|[1-4][0-9]{3}|5[0-4][0-9]{2}|55[0-4][0-9]|555[0-5])/ (okay, I get the point!)

The numbers are contrived, but they're also really basic. In the real world you might need to generate a regex on-the-fly for validation.

Learn more

If you're interested in learning more aboutcharacter classes and other regex features, I personally have always foundregular-expressions.info to be pretty useful.

As of April 07, 2019, this library runs>1m test assertions against generated regex-ranges to provide brute-force verification that results are correct.

Tests run in ~280ms on my MacBook Pro, 2.5 GHz Intel Core i7.

Generated regular expressions are optimized:

• duplicate sequences and character classes are reduced using quantifiers
• smart enough to use? conditionals when number(s) or range(s) can be positive or negative
• uses fragment caching to avoid processing the same exact string more than once

Pull requests and stars are always welcome. For bugs and feature requests,please create an issue.

Running and reviewing unit tests is a great way to get familiarized with a library and its API. You can install dependencies and run tests with the following command:

$ npm install&& npmtest

(This project's readme.md is generated byverb, please don't edit the readme directly. Any changes to the readme must be made in the.verb.md readme template.)

To generate the readme, run the following command:

$ npm install -g verbose/verb#dev verb-generate-readme&& verb