JavaScript Object Methods

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JavaScript Object Methods



Example

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

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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:
The JavaScript this Tutorial


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

Example

name = person.fullName;
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Adding a Method to an Object
Adding a new method to an object is easy:

Example

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

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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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Reference: https://www.w3schools.com/js/js_object_methods.asp