Run a RegEx replace on a RegEx in Javascript

Question

I have the regex:

var reValid = /^\s*(?:'[^'\\]*(?:\\[\S\s][^'\\]*)*'|[^,'\s\\]*(?:\s+[^,'\s\\]+)*)\s*(?:,\s*(?:'[^'\\]*(?:\\[\S\s][^'\\]*)*'|[^,'\s\\]*(?:\s+[^,'\s\\]+)*)\s*)*$/;

Which validates a CSV file, but I want to be able to modify the delimiter (') with any delimiter.

Is it possible to run a regex replace on a regex?

Example - use a backtick (`) as the delimiter:

var reValid = /^\s*(?:`[^`\\]*(?:\\[\S\s][^`\\]*)*`|[^,`\s\\]*(?:\s+[^,`\s\\]+)*)\s*(?:,\s*(?:`[^`\\]*(?:\\[\S\s][^`\\]*)*`|[^,`\s\\]*(?:\s+[^,`\s\\]+)*)\s*)*$/;

It is possible but could lead to unexpected behaviour... Build the regex using a variable for the delimiter and the RegExp object. That ensures only the positions that need the delimiter are affected. — sg3s
– sg3s, Commented Apr 22, 2012 at 7:13

Paul · Accepted Answer · 2012-04-22 07:08:45Z

4

Sure, just use the source property to get the expression as a string, do your replacement, and then create a new RegExp object with the new expression:

var reValid = /^\s*(?:'[^'\\]*(?:\\[\S\s][^'\\]*)*'|[^,'\s\\]*(?:\s+[^,'\s\\]+)*)\s*(?:,\s*(?:'[^'\\]*(?:\\[\S\s][^'\\]*)*'|[^,'\s\\]*(?:\s+[^,'\s\\]+)*)\s*)*$/;
reValid = RegExp(reValid.source.replace(/'/g, '`'));

edited Apr 22, 2012 at 7:08

answered Apr 22, 2012 at 7:02

Paul

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1 Comment

Evan Plaice Over a year ago

One issue, if the original regex has modifiers /[regex]/g you need to re-add them. It doesn't apply to the example I posted.

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