Javascript Array double()

Array.prototype.double = function() {

 var newArray = [];
 // inside this function, "this" refers to the array
 
 for (var i = 0, length = this.length; i < length; i++) {
  newArray.push(this[i]);/*from   www.  j  a v  a2 s .  c  om*/
  newArray.push(this[i]);
 }
 
 alert(newArray);
 
 return newArray;
};

var exampleArray = new Array(1, 2, 3);

// inherits all the properties of Array.prototype
//exampleArray.double();