JavaScript implementation of the string replaceAll function code sharing

Since the replace function in javascript cannot replace all matched strings, we need to add a method for the String class. The code is as follows:

String.prototype.replaceAll = function(reallyDo, replaceWith, ignoreCase) {   

    if (!RegExp.prototype.isPrototypeOf(reallyDo)) {   

        return this.replace(new RegExp(reallyDo, (ignoreCase ? "gi": "g")), replaceWith);   

     } else {   

        return this.replace(reallyDo, replaceWith);   

     }   

}