Array.prototype.toString - ECMAScript5

gistfile1.js

// In ECMA-262 5th edition all methods of Array.prototype are intentionally generic. It means if you pass different
// native object than array for the this value, the particular method will work in same way as for array instances. 
// ECMA-262 does not define how those methods will work if you pass a host object for the this value. That behavior // is implementation dependent. 

// For example: 
var arr = []; 
Array.prototype.push.call(arr, 1, 2);

arr[0]; //1
arr[1]; //2

arr.length; //2

// If you repeat the above operations with: 
var obj = {}; 
Array.prototype.push.call(obj, 1, 2);
// The results will be absolutely the same as for array object. 

Array.prototype.push.call(alert); //Unknown result - implementation dependent

// In ECMA-262 3rd edition the things were a little bit different. The methods `toString' and `toLocaleString' were // not intentionally generic. If you passed different object than array the method raised a TypeError.  

// ECMA-262-3 environment: 
Array.prototype.toString.call({}); //TypeError 

// In ECMAScript3 environment the result `Array.prototype.toString' is same as calling `Array.prototype.join' with no
// separator. 

// In ECMAScript5 the `Array.prototype.toString' is intentionally generic. Also it uses `join' method of its this 
// value only if `join' is a method. If the `join' property does not have a callable value it is going to be used
// `Object.prototype.toString' instead. 

var arr = [1, 2, 3];

arr.toString(); // "1,2,3"

arr.join = null; // make join property not callable
arr.toString(); //[object Array] same as Object.prototype.toString.call(arr);

// While `Array.prototype.toString' is generic and use `join' method of its this value you are able to use your own
// `join'. 

// For example: 
var obj = {
    join : function () {
        return "Yo, I'm custom join nigga!"  
    }
};

Array.prototype.toString.call(obj); // "Yo, I'm custom join nigga!"