Tutorials

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

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;}

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"};
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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"
};
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Accessing Object Properties

 

You can access object properties in two ways:

objectName.propertyName

or

objectName["propertyName"]

Example1

person.lastName;
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Example2

person["lastName"];
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Accessing Object Methods

 

You access an object method with the following syntax:

objectName.methodName()

Example

name = person.fullName();
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If you access the fullName method, without (), it will return the function definition:

Example

name = person.fullName;
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A method is actually a function definition stored as a property value.

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.

You will learn more about objects later in this tutorial.

Test Yourself with Exercises