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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 = Fiat

car.model = 500

car.weight = 850kg

car.color = white

car.start()

car.drive()

car.brake()

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 (Fiat) to a variable named car:

var car = "Fiat";

Try it Yourself »

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

This code assigns many values (Fiat, 500, white) to a variable named car:

var car = {type:"Fiat", model:500, color:"white"};

Try it Yourself »

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

Note JavaScript objects are containers for named values.


Object Properties

The name:values pairs (in JavaScript objects) are called properties.

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

Property Property Value
firstName John
lastName Doe
age 50
eyeColor blue


Object 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;}

Note JavaScript objects are containers for named values, called properties and 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"};

Try it Yourself »

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"
};

Try it Yourself »


Accessing Object Properties

You can access object properties in two ways:

objectName.propertyName

or

objectName[propertyName]

Example1

person.lastName;

Try it Yourself »

Example2

person["lastName"];

Try it Yourself »


Accessing Object Methods

You access an object method with the following syntax:

objectName.methodName()

Example

name = person.fullName();

Try it Yourself »

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

Example

name = person.fullName;

Try it Yourself »


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.

Note You will learn more about objects later in this tutorial.



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