[].slice

Array-like Objects in JavaScript - Blog - ShiftEleven
slice
this extracts a section of an array and returns a new array, and without a beginning and ending index, it simply returns a copy of the array

var $A = function(obj) {   
   return Array.prototype.slice.call(obj);   
};  
 // Example usage:  
$A(document.getElementsByTagName("li"));

JavaScript数组操作 - Richie - 博客园

//Supported by Firefox, IE6, IE7, Opera, Safari
var arrayLike = { 0:"ccc", 1:1, 2:"eee", 3:8, length:4 }; //an object that looks like an object
var trueArray = [].slice.call(arrayLike, 2, arrayLike.length); //make a new array with arrayLike
trueArray.push("2008-02-12");
document.write(trueArray.join(" | ")); //result: eee | 8 | 2008-02-12
document.write("
");

Array.prototype.map = function(callback){
    if(!callback || typeof callback!="function") return this;
    for(var i=0; i<this.length; i++) callback( this[i], i);
    return this;
};