Javascript String indexOf(s, fromIndex)

String.prototype.indexOf = function(s, fromIndex) {
  if (!fromIndex) {
    fromIndex = 0;/*from w w  w.  j av  a  2 s  .  c om*/
  }
  
  var idx = -1;
  for (var i = fromIndex, len = this.length; i < len; i++) {
    var matches = true;
    for (var j = 0, len2 = s.length; j < len2; j++) {
      if (this[i + j] != s[j]) {
        matches = false;
        break;
      }
    }
    if (matches) {
      idx = i;
      break;
    }
  }
  
  return idx;
};