if (!Array.prototype.indexOf){
  Array.prototype.indexOf = function(elt /*, from*/){
    var len = this.length >>> 0;

    var from = Number(arguments[1]) || 0;
    from = (from < 0)
         ? Math.ceil(from)
         : Math.floor(from);
    if (from < 0)
      from += len;

    for (; from < len; from++){
      if (from in this && this[from] === elt)
        return from;
    }
    return -1;
  };
}