CODEWITHSUNDEEP
javascriptregex
user2305193
user2305193

Reputation: 2059

How to convert a regular expression to a String literal and back again?

How can I:

  1. Convert a JavaScript RegExp with flags to a String literal (think JSON),
  2. And convert that literal back to a regex?

For example with the String "the weather is nice today":

var myRe = new RegExp("weather","gi");
var myReToString = myRe.toString(); // myReToString is now "/weather/gi"

var myReCopy = /* How to get this copy only from myReToString ? */

To modify the original RegExp properties see torazaburo's answer.

Upvotes: 9

Views: 5280

Answers (3)

user663031
user663031

Reputation:

Take a look at the accessor properties on the RegExp prototype such as source and flags. So you can do:

var myRe = new RegExp("weather", "gi")

var copyRe = new RegExp(myRe.source, myRe.flags);

For the spec see http://www.ecma-international.org/ecma-262/6.0/#sec-get-regexp.prototype.flags.

Serializing and deserializing regexps

If your intent in doing this is to serialize the regexp, such as into JSON, and then deserialize it back, I would recommend storing the regexp as a tuple of [source, flags], and then reconstituting it using new RexExp(source, flags). That seems slightly cleaner than trying to pick it apart using regexp or eval'ing it. For instance, you could stringify it as

function stringifyWithRegexp(o) {
  return JSON.stringify(o, function replacer(key, value) {
    if (value instanceof RegExp) return [value.source, value.flags];
    return value;
  });
}

On the way back you can use JSON.parse with a reviver to get back the regexp.

Modifying regexps

If you want to modify a regexp while retaining the flags, you can create a new regexp with modified source and the same flags:

var re = /weather/gim;
var newre = new RegExp(re.source + "| is", re.flags);

Upvotes: 7

falsetru
falsetru

Reputation: 369134

You can use eval to get back the regular expression:

var myRe = RegExp("weather", "gi");
var myReString = myRe.toString();
eval(myReString); // => /weather/gi

NOTE: eval can execute arbitrary javascript expression. Use eval only if you're sure the string is generated from regular expression toString method.

Upvotes: 3

GingerPlusPlus
GingerPlusPlus

Reputation: 5616

I'm not sure if this code works in all cases, but I'm sure that this can be done using regex:

var regex = new RegExp('^/(.+)/(.*)$')
function stringToRegex(s) {
    var match = s.match(regex)
    return new RegExp(match[1], match[2])
}

var test = new RegExp("weather", "gi")

console.log(stringToRegex(test.toString()))
console.log(stringToRegex(test.toString()).toString() === test.toString())

Regular expression visualization

Debuggex Demo

Upvotes: 3

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