this in JavaScript Objects

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What is this?

In JavaScript, the this keyword refers to an object.

The this keyword refers to different objects depending on how it is used:

Alone, this refers to the global object.

In a function, this refers to the global object.

In a function, in strict mode, this is undefined.

In an object method, this refers to the object.

In an event, this refers to the element that received the event.

Methods like call(), apply(), and bind() can refer this to any object.

Note

this is not a variable.

this is a keyword.

You cannot change the value of this.

this in a Method

When used in an object method, this refers to the object.

In the example on top of this page, this refers to the person object.

Because the fullName method is a method of the person object.

Example

const person = {
firstName: "John",
  lastName : "Doe",
id       : 5566,
fullName : function() {
    return this.firstName + " " + this.lastName;
  }
};

Try it Yourself »

Object Method Binding

In these examples, this is the person object:

Example

const person = {
firstName : "John",
lastName   : "Doe",
id         : 5566,
myFunction : function() {
    return this;
  }
};

Try it Yourself »

Example

const person = {
firstName: "John",
lastName : "Doe",
id       : 5566,
fullName : function() {
    return this.firstName + " " + this.lastName;
  }
};

Try it Yourself »

i.e. this.firstName is the firstName property of this (the person object).

Explicit Function Binding

The call() and apply() methods are predefined JavaScript methods.

They can both be used to call an object method with another object as argument.

Function Borrowing

With the bind() method, an object can borrow a method from another object.

This example creates 2 objects (person and member).

The member object borrows the fullname method from the person object:

Example

const person = {
  firstName:"John",
  lastName: "Doe",
fullName: function () {
    return this.firstName + " " + this.lastName;
  }
}

const member = {
  firstName:"Hege",
  lastName: "Nilsen",
}

let fullName = person.fullName.bind(member);

Try it Yourself »

This Precedence

Use the following precedence of order to determine which object this refers to:

Order	Object	Because
1	bind()	`this` is in a function being called using bind()
2	apply()	`this` is in a function being called using apply()
2	call()	`this` is in a function being called using call()
3	Object method	`this` is in an object function (method)
4	Global scope	`this` is in a function in the global scope