Adding modifiers to an existing regular expression

Question

I have a bunch of regular expressions like lower = /[a-z]/ Later in my program i need to use this as /[a-z]/g ie. i need to add the 'global' modifier later. So how to add a modifier to an existing regular expression?

Answer 1

Use RegEx source and flags to separate the regular expression from the flags. Then create a new one with the string and set the needed flags.

var re = /^[a-z]*$/;
var re2 = new RegExp(re.source, re.flags + "i");

console.log( re.test("abc") )
console.log( re.test("ABC") )
console.log( re2.test("abc") )
console.log( re2.test("ABC") )

Answer 2

Here is a function to build on epascarello's answer and the comments. You said you have quite a few of regexps to modify later on, you could just redefine the variable they are referenced in or make some new ones with a function call.

function modifyRegexpFlags(old, mod) {
    var newSrc = old.source;
    mod = mod || "";
    if (!mod) {
        mod += (old.global) ? "g" : "";
        mod += (old.ignoreCase) ? "i" : "";
        mod += (old.multiline) ? "m" : "";
    }
    return new RegExp(newSrc, mod);
}

var lower = /[a-z]/;
//Some code in-between
lower = modifyRegexpFlags(lower, "g");

If the second argument is omitted, the old modifiers will be used.
(Credit to davin for the idea).

Answer 3

You can write a method for it-

RegExp.prototype.reflag= function(flags){
    return RegExp(this.source, flags);
}