JavaScript Objects

Real Life Objects, Properties, and Methods

In real life, a car is an object.

A car has properties like weight and color, and methods like start and stop:

Object	Properties	Methods
	car.name = Ford	car.start()
	car.model = Mustang	car.drive()
	car.weight = 850kg	car.brake()
	car.color = blue	car.stop()

All cars have the same properties, but the property values differ from car to car.

All cars have the same methods, but the methods are performed at different times.

JavaScript Objects

You have already learned that JavaScript variables are containers for data values.

This code assigns a simple value (Ford) to a variable named car:

var car =
                "Ford";

Objects are variables too. But objects can contain many values.

This code assigns many values (Ford, Mustang, blue) to a variable named car:

var car = {type:"Ford", model:"Mustang", color:"blue"};

The values are written as name:value pairs (name and value separated by a colon).

JavaScript objects are containers for named values called properties or methods.

Object Definition

You define (and create) a JavaScript object with an object literal:

Example

var person = { firstName:"John", lastName:"Doe", age:50, eyeColor:"blue" };

Spaces and line breaks are not important. An object definition can span multiple lines:

Example

var person = {

                  firstName:"John",

                  lastName:"Doe",

                  age:50,

                  eyeColor:"blue"
};

Object Properties

The name:values pairs in JavaScript are called properties:

Property	Property Value
firstName	John
lastName	Doe
age	50
eyeColor	blue

Accessing Object Properties

You can access object properties in two ways:

objectName.propertyName

or

objectName["propertyName"]

Example 1

person.lastName;

Example 2

person["lastName"];

Object Methods

Objects can also have methods.

Methods are actions that can be performed on objects.

Methods are stored in properties as function definitions.

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

A method is a function stored as a property.

Example

var person = {

                  firstName:"John",

                  lastName:"Doe",

                  id:5566,

                  fullName:function() {

                   
                return this.firstName +
                " " +
                this.lastname;

                  }
};

The this Keyword

In a function definition, this refers to the "owner" of the function.

In the example above, this is the person object that "owns" the fullName function.

In other words, this.firstName means the firstName property of this object.

Read more about the this keyword at JS this Keyword

Accessing Object Methods

You access an object method with the following syntax:

objectName.methodName()

Example

name = person.fullName();

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

Example

name = person.fullName;

Do Not Declare Strings, Numbers, and Booleans as Objects!

When a JavaScript variable is declared with the keyword "new", the variable is created as an object:

var x =
                new String();
                // Declares x as a String object
var y =
                new Number();
                // Declares y as a Number object
var z =
                new Boolean();
                // Declares z as a Boolean object

Avoid String, Number, and Boolean objects. They complicate your code and slow down execution speed.

Reference

All the documentation in this page is taken from w3schools.com