String.prototype.replace

String.prototype.replace = function(re, str){
  var replace = function(t, b, a){
    var i = t.indexOf(b), n = i+b.length-t.length;
    return (i !== -1)? t.slice(0,i) + a + ((n<0)? t.slice(n) : '') : t;
  }, ret;
 
  if(typeof re === 'string'){
    ret = replace(this, re, str);
  }else if(re instanceof RegExp){
    ret = this; var ba = ret.match(re), l = ba.length, i;
    for(i=0;i<l;i++){ret = replace(ret, ba[i], str);}
  }else{
    ret = this;
  }
  return ret.toString();
};