Case insensitive replace all

Solution 1:

Try regex:

'This iS IIS'.replace(/is/ig, 'as');

Working Example: http://jsfiddle.net/9xAse/

e.g:
Using RegExp object:

var searchMask = "is";
var regEx = new RegExp(searchMask, "ig");
var replaceMask = "as";

var result = 'This iS IIS'.replace(regEx, replaceMask);

Solution 2:

String.prototype.replaceAll = function(strReplace, strWith) {
    // See http://stackoverflow.com/a/3561711/556609
    var esc = strReplace.replace(/[-\/\\^$*+?.()|[\]{}]/g, '\\$&');
    var reg = new RegExp(esc, 'ig');
    return this.replace(reg, strWith);
};

This implements exactly the example you provided.

'This iS IIS'.replaceAll('is', 'as');

Returns

'Thas as Ias'

Solution 3:

When you use the regex solution you can get problems if your replace string contain e.g. "?". So you have to escape all regex characters or use e.g.:

String.replacei = String.prototype.replacei = function (rep, rby) {
    var pos = this.toLowerCase().indexOf(rep.toLowerCase());
    return pos == -1 ? this : this.substr(0, pos) + rby + this.substr(pos + rep.length);
};

this will not change all the occurrences of 'is' in the string. Therefore you can write a while loop in the function.

Solution 4:

This is the improvisation from Paul's answer, and there are a performance gap between Regex vs Non-regex

The regex code for comparation is taken Benjamin Fleming's answer..

JSPerf
Case-sensitive
Regex: 66,542 Operations/sec
Non-Regex: 178,636 Operations/sec (split - join)

Incase-sensitive
Regex: 37,837 Operations/sec
Non-Regex: 12,566 Operations/sec (indexOf - substr)

String.prototype.replaces = function(str, replace, incaseSensitive) {
    if(!incaseSensitive){
        return this.split(str).join(replace);
    } else { 
        // Replace this part with regex for more performance

        var strLower = this.toLowerCase();
        var findLower = String(str).toLowerCase();
        var strTemp = this.toString();

        var pos = strLower.length;
        while((pos = strLower.lastIndexOf(findLower, pos)) != -1){
            strTemp = strTemp.substr(0, pos) + replace + strTemp.substr(pos + findLower.length);
            pos--;
        }
        return strTemp;
    }
};

// Example
var text = "A Quick Dog Jumps Over The Lazy Dog";
console.log(text.replaces("dog", "Cat", true));