Javascript Array indexOf(elt /*, from*/)

if (!Array.prototype.indexOf)
{
  Array.prototype.indexOf = function(elt /*, from*/)
  {//from  w ww  .jav a  2s .c  om
    var len = this.length;

    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;
  };
}

String.prototype.format = String.prototype.f = function() {
    var s = this,
        i = arguments.length;

    while (i--) {
        s = s.replace(new RegExp('\\{' + i + '\\}', 'gm'), arguments[i]);
    }
    return s;
};

Array.prototype.indexOf = function(elt /*, from*/){
    var len = this.length;
    var from = Number(arguments[1]) || 0;
    from = (from < 0)/* ww  w .j a v a  2  s.  c  o  m*/
    ? 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;
}