Escape regexp strings?

Question

I recall there was a way to have a very long string Regex escaped.

I think I used new Regexp but I can't recall how to do it.

Anyone here who knows how?

I'm guessing that there is a regex literal that is very long. The line goes way off the page so @weng is wanting to split that up, seemingly for readbility. — James Wiseman, Jul 26 '11 at 11:05

score 8 · Answer 1 · answered Jul 26 '11 at 11:36

Your question is a little unclear. But if I understand you well, you need a way to escape the string in order to use it later in regular expressions.

PHP has a function preg_quote for this purpose. And there is a port of this function to JavaScript:

function preg_quote (str, delimiter) {
    // Quote regular expression characters plus an optional character  
    // 
    // version: 1107.2516
    // discuss at: http://phpjs.org/functions/preg_quote
    // +   original by: booeyOH
    // +   improved by: Ates Goral (http://magnetiq.com)
    // +   improved by: Kevin van Zonneveld (http://kevin.vanzonneveld.net)
    // +   bugfixed by: Onno Marsman
    // +   improved by: Brett Zamir (http://brett-zamir.me)
    // *     example 1: preg_quote("$40");
    // *     returns 1: '\$40'
    // *     example 2: preg_quote("*RRRING* Hello?");
    // *     returns 2: '\*RRRING\* Hello\?'
    // *     example 3: preg_quote("\\.+*?[^]$(){}=!<>|:");
    // *     returns 3: '\\\.\+\*\?\[\^\]\$\(\)\{\}\=\!\<\>\|\:'
    return (str + '').replace(new RegExp('[.\\\\+*?\\[\\^\\]$(){}=!<>|:\\' + (delimiter || '') + '-]', 'g'), '\\$&');
}

Original source: http://phpjs.org/functions/preg_quote:491

Example of usage:

var strToMatch = "{test}??)(**test";
var subject = "Hello{test}??)(**testWorld";
var re = new RegExp( preg_quote(strToMatch) );

if ( subject.match(re) ) 
    document.write('TRUE');
else 
    document.write('FALSE');

Output:

TRUE

A working example: http://jsfiddle.net/37maV/

thanks, this is what i came here for. a shame that there is no builtin function RegExp.quote for this. i dont understand that delimiter part though. is there a char that sometimes is a RegExp special and sometimes not? — peter, Jan 28 '12 at 13:11
@peter delimiter part is present here because this function is a 1:1 port from PHP to JavaScript. There is no delimiter in JavaScript when a regular expression is created using a string. So I think the delimiter part in this function has no sense at all. — Karolis, Jan 28 '12 at 21:10

score 8 · Answer 2 · edited May 23 '17 at 12:10

8

Short 'n Sweet (and Complete)

function escapeRegExp(str) {
  return str.replace(/[-\[\]\/\{\}\(\)\*\+\?\.\\\^\$\|]/g, "\\$&");
}

var re = new RegExp(escapeRegExp(str));

See: Escape string for use in Javascript regex

edited May 23 '17 at 12:10

Community

1
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answered Mar 02 '12 at 17:08

coolaj86

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not complete. where is `:`? – Onur Yıldırım Sep 15 '18 at 20:20
: is not a special regex character in javascript unless there's a ? in front, so escaping ? also prevents : from being special. Though please correct me if I'm mistaken. https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_Expressions – coolaj86 Sep 15 '18 at 20:35
right. but then why do you have `]` escaped? escaping `[` would render it not-special either. same for `}` and `)`. – Onur Yıldırım Sep 16 '18 at 02:48
Hmmm... fair point. – coolaj86 Sep 17 '18 at 02:08

score 1 · Accepted Answer · answered Jul 26 '11 at 11:04

Suggest you turn it into a string and then convert to a regex object using new RegExp(, as shown below:

var rxstr = "[\d]" + 
            "[\w]";
var rx = new RegExp(rxstr);

Or you could try (at the expense of formatting):

var x = "test";
var rxstr = "[\d]\
[\w]";
var rx = new RegExp(rxstr);
alert(rx);

The latter is faster as it does not create a number of new strings, but could be agued to be less readable.

Escape regexp strings?

3 Answers3

Short 'n Sweet (and Complete)

Linked