String.prototype.replaceAll

 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);   
    }   
}