gistfile1.js

if (Array.prototype.map === undefined) {
  Array.prototype.map = function(callback) {
    var len = this.length;
      if (typeof callback != "function") {
          throw new TypeError();
      }
      
    var mapped = [len],
        o = arguments[1];
    for (var i = 0; i < len; i++) {
        if (i in this) {
            mapped[i] = callback.call(o, this[i], i, this);
        }    
    }

    return mapped;
  };
}