Understand and apply the call and apply in JavaScript

Call is in order to change the context of a function, in other words, to change the direction of this inside the function. Because JavaScript has a "context of definition", "Runtime Context" and "context" can be changed. For example: var func1 = function (Arg1, arg2) {};

Can be passed Func1.call (this, arg1, arg2); Or func1.apply (this, [Arg1, arg2]); To invoke. Where this is the context you want to specify, he can have any JavaScript object (everything in JavaScript), call needs to pass the parameters in order, and apply is to put the parameters in the array.

In JavaScript, the number of parameters of a function is not fixed, so to say the applicable conditions, when your parameters are clearly known quantity, with call, but not sure, with apply, and then put the parameter push into the array to pass in.  When the number of arguments is indeterminate, the arguments can also be used to facilitate all parameters within the function. In JavaScript oop, we often define this:

function Cat () {
}
cat.prototype={
Food: "Fish",
Say:function () {
Alert ("I Love" +this.food);
}
}
var blackcat = new Cat;
Blackcat.say ();

But if we have an object Whitedog = {food: "Bone"}, we do not want to redefine it say method, then we can use call or Apply with Blackcat say method: BlackCat.say.call (Whitedog );

So, you can see that call and apply are meant to change this dynamically, and when an object does not have a method, but the others, we can use call or apply to manipulate other objects.

The DOM node chosen by document.getElementsByTagName is a type of array that is similar to array. It cannot apply methods such as Push,pop under the array. We can do this by:
var domnodes = Array.prototype.slice.call (document.getElementsByTagName ("*"));
This allows the domnodes to apply all the methods under the array.
Source: http://www.zhihu.com/question/20289071

Understand and apply the call and apply in JavaScript