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JavaScript Object Methods

Example

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

What is this?

In JavaScript, the this keyword refers to an object.

Which object depends on how this is being invoked (used or called).

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

In an object method, this refers to the object.
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 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. It is a keyword. You cannot change the value of this.

See Also:

JavaScript Methods

JavaScript methods are actions that can be performed on objects.

A JavaScript method is a property containing a function definition.

Property Value
firstName John
lastName Doe
age 50
eyeColor blue
fullName function() {return this.firstName + " " + this.lastName;}

Methods are functions stored as object properties.

Accessing Object Methods

You access an object method with the following syntax:

objectName.methodName()

You will typically describe fullName() as a method of the person object, and fullName as a property.

The fullName property will execute (as a function) when it is invoked with ().

This example accesses the fullName() method of a person object:

Example

name = person.fullName();

If you access the fullName property, without (), it will return the function definition:

Example

name = person.fullName;

Adding a Method to an Object

Adding a new method to an object is easy:

Example

person.name = function () {
  return this.firstName + " " + this.lastName;
};

Using Built-In Methods

This example uses the toUpperCase() method of the String object, to convert a text to uppercase:

let message = "Hello world!";
let x = message.toUpperCase();

The value of x, after execution of the code above will be:

HELLO WORLD!

Example

person.name = function () {
  return (this.firstName + " " + this.lastName).toUpperCase();
};

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