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Example

<!DOCTYPE html>

<html>

<body>

<h1>The JavaScript <i>this</i> Keyword</h1>

<p>In this example, <b>this</b> refers to the <b>person</b> object.</p>

<p>Because <b>fullName</b> is a method of the person object.</p>

<p id=”demo”></p>

<script>

// Create an object:

const person = {

  firstName: “John”,

  lastName: “Doe”,

  id: 5566,

  fullName : function() {

    return this.firstName + ” ” + this.lastName;

  }

};

// Display data from the object:

document.getElementById(“demo”).innerHTML = person.fullName();

</script>

</body>

</html>

Output

The JavaScript this Keyword

In this example, this refers to the person object.

Because fullName is a method of the person object.

John Doe

What is this?

In JavaScript, this keyword refers to an object.

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

  • In an object method, this refers to the object.
  • 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 to any object.

JavaScript Methods

JavaScript methods are defined as actions that can be performed on objects.

A JavaScript method is a property that consists of a function definition.

Property

Value

firstName

John

lastName

Doe

age

50

eyeColor

blue

fullName

function() {return this.firstName + ” ” + this.lastName;}

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 is executed (as a function) when it is invoked with ().

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

Example

<!DOCTYPE html>

<html>

<body>

<h2>JavaScript Objects</h2>

<p>Creating and using an object method.</p>

<p>A method is actually a function definition stored as a property value.</p>

<p id=”demo”></p>

<script>

const person = {

  firstName: “John”,

  lastName: “Doe”,

  id: 5566,

  fullName: function() {

    return this.firstName + ” ” + this.lastName;

  }

};

document.getElementById(“demo”).innerHTML = person.fullName();

</script>

</body>

</html>

Output

JavaScript Objects

Creating and using an object method.

A method is actually a function definition stored as a property value.

John Doe

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

Example

<!DOCTYPE html>

<html>

<body>

<h2>JavaScript Objects</h2>

<p>An object method is a function definition stored as a property value.</p>

<p>If you access it without (), it will return the function definition:</p>

<p id=”demo”></p>

<script>

const person = {

  firstName: “John”,

  lastName: “Doe”,

  id: 5566,

  fullName: function() {

    return this.firstName + ” ” + this.lastName;

  }

};

document.getElementById(“demo”).innerHTML = person.fullName;

</script>

</body>

</html>

Output

JavaScript Objects

An object method is a function definition stored as a property value.

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

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

Adding a Method to an Object

Adding a new method to an object is easy:

Example

<!DOCTYPE html>

<html>

<body>

<h2>JavaScript Objects</h2>

<p id=”demo”></p>

<script>

const person = {

  firstName: “John”,

  lastName: “Doe”,

  id: 5566,

};

person.name = function() {

  return this.firstName + ” ” + this.lastName;

};

document.getElementById(“demo”).innerHTML =

“My father is ” + person.name();

</script>

</body>

</html>

Output

JavaScript Objects

My father is John Doe

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

<!DOCTYPE html>

<html>

<body>

<h2>JavaScript Objects</h2>

<p id=”demo”></p>

<script>

const person = {

  firstName: “John”,

  lastName: “Doe”,

  id: 5566,

};

person.name = function() {

  return (this.firstName + ” ” + this.lastName).toUpperCase();

};

document.getElementById(“demo”).innerHTML =

“My father is ” + person.name();

</script>

</body>

</html>

Output

JavaScript Objects

My father is JOHN DOE


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