what's the difference between 'call/apply' and 'bind' [duplicate]

Question

var obj = {    x: 81,    getX: function() {       console.log( this.x)     } }; var getX = obj.getX.bind(obj);//use obj as 'this'; getX();//81 var getX = function(){   obj.getX.apply(obj);  } getX();//also 81 

The use of bind and call/apply look very similar, I want to know what's the difference between them.The two getX Function above is the same?

Answer 1

bind returns a function which will act like the original function but with this predefined. It is usually used when you want to pass a function to an event handler or other async callback.

call and apply will call a function immediately letting you specify both the value of this and any arguments the function will receive.

Your second example defines an anonymous function which calls apply. This is a common pattern; bind provides a standard implementation of that which allows you to do it with a simple function call (thus being quicker and easier to write).

Answer 2

.call() - calls the same function with the specified arguments

.apply() - calls the same function with the arguments specified in an array

.bind() - creates a new function with the same function body, with a preset value of this (the first argument) and returns that function.

In all cases, the first argument is used as the value of this inside the function.