Question

Is it possible to do something like this?

var pattern = /some regex segment/ + /* comment here */     /another segment/; 

Or do I have to use new RegExp() syntax and concatenate a string? I’d prefer to use the literal as the code is both more self-evident and concise.

Answer 1

Here is how to create a regular expression without using the regular expression literal syntax. This lets you do arbitrary string manipulation before it becomes a regular expression object:

var segment_part = "some bit of the regexp"; var pattern = new RegExp("some regex segment" + /*comment here */               segment_part + /* that was defined just now */               "another segment"); 

If you have two regular expression literals, you can in fact concatenate them using this technique:

var regex1 = /foo/g; var regex2 = /bar/y; var flags = (regex1.flags + regex2.flags).split("").sort().join("").replace(/(.)(?=.*\1)/g, ""); var regex3 = new RegExp(regex1.source + regex2.source, flags); // regex3 is now /foobar/gy 

It’s just more wordy than just having expression one and two being literal strings instead of literal regular expressions.