How to access the correct `this` inside a callback?

In JavaScript, ‘this’ behaves differently compared to other programming languages. If we are performing a normal function call then ‘this’ points to the window object. But we are calling the function differently than ‘this’ will point to a near object. To understand it better below we elaborated with two code snippets with two different call approaches.

Example 1: When we call a function in a normal way in the below example

Javascript

function printThis(){

  console.log(this);

}

printThis();

Output:

Window {0: Window, window: Window, 
        self: Window, document: document, 
        name: '', location: Location, …}

Example 2: When we call a function using object notation.

Javascript

var obj={
 name: "Ramesh",
 printThis: function(){
    console.log(this);
 }
}
obj.printThis();

Output:

{name: 'Ramesh', printThis: ƒ}

So, from the above two examples, we can clearly understand the behavior of ‘this’ when we make different types of function calls. 

Approach: First create an object and enter sample properties. Make sure you add a function for one key, in that function add a callback function using setTimeout. Inside this setTimeout function use ‘bind’ to bind the context of this after then return this.

Example: Using Bind

Javascript

var outerFunction= function(){
   innerFunction = function() {
   };
    setTimeout(innerFunction.bind(this),2000);
     return this;
};

var obj = { method: outerFunction ,company :'geeksforgeeks'} ;
obj.method();

Output: