Now I understand the power of bind method how it will always run in the given context.

gistfile1.txt

For example, take a look at the first example below: 
1)(function(){
	var cart={
		item: "product1",
		price: 35.50,
		quantity: 2,
		buying: function(){
			alert("you bought"+this.item);
		}
	};
	//cart.buying=cart.buying.bind(cart)

	var text=document.getElementById("text");
	text.addEventListener("click",cart.buying);

})();

If you run this without the bind method, it will NOT print out the value of a property named item. Instead it will print out undefined because it is only passing a reference to the function. !!