"reverse" regular expression with JavaScript(node.js)

Question

With regular expression like this /\w/ I can match strings like a, q. Is there any idiomatic way to generate all the strings which match some regex in JS?

Don't think about infinite cases. I just want to describe some sets of possible symbols briefly.

something meaningful instead of

var s = ' !"#$%&\'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|}~'

This is a hard problem to solve. As there are infinite regular expressions that have infinite strings they match (for example /a+/). — Jozef Legény
– Jozef Legény, Commented Mar 4, 2016 at 15:37
That program would very easy not halt anymore, a \w+ is all you need to generate an "infinite" amount of strings. — crackmigg
– crackmigg, Commented Mar 4, 2016 at 15:38
And Python xeger, too. Oh, just came across randexp for JS. randexp will generate a random string that matches a given RegExp Javascript object. — Wiktor Stribiżew
– Wiktor Stribiżew, Commented Mar 4, 2016 at 15:42
Another link (regldg): This is a C based solution available for download and as web service (with restricted size of output) to test the functionality online. I have no affiliation whatsoever with the project. — collapsar
– collapsar, Commented Mar 4, 2016 at 16:13

Wiktor Stribiżew · Accepted Answer · 2016-03-04 15:50:16Z

9

You can try the randexp library:

Randexp will generate a random string that matches a given RegExp Javascript object

See the demo:

document.body.innerHTML = new RandExp(/\w/).gen();
document.body.innerHTML += "<br/>" + new RandExp(/\w/).gen();
document.body.innerHTML += "<br/>" + new RandExp(/[for]{3}/).gen();
document.body.innerHTML += "<br/>" + new RandExp(/I like (cats|dogs|mice)/).gen();

<script src="https://github.com/fent/randexp.js/releases/download/v0.4.1/randexp.min.js"></script>

edited Mar 4, 2016 at 15:50

answered Mar 4, 2016 at 15:48

Wiktor Stribiżew

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5 Comments

Wiktor Stribiżew Over a year ago

You'd need to generate any chunk of text and test against the regexp. It is not possible nowadays, I think, you'd have to wait for ages. Why do you need to get all possible variations? You just need that for testing, don't you?

Wiktor Stribiżew Over a year ago

Again, that is not possible.

kharandziuk Over a year ago

Why? I don't need to describe infinite cases. I just need to say /[\w\{\}}]/ instead of writing string like abcdef ..... {}

Wiktor Stribiżew Over a year ago

So, what prevents you from writing /[\w{}]/ manually? Regexps are meant to extract strings meeting specific patterns, not the other way round. The "other way round" is testing regexps, and what I suggest in the answer meets this end, I believe.

Wiktor Stribiżew Over a year ago

I mean to say that using the regexp the way you want is something what regex is not supposed to do. Saying "it is not possible" I mean it is not that easy to re-construct the regex parser (although it is feasible) and try to produce all substrings using the Unicode sets. Just that means a lot of work, and without some considerable effort, that is rather a broad topic for this Q&A site.

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