In JavaScript, almost "everything" is an object.

• Booleans can be objects (or primitive data treated as objects)

• Numbers can be objects (or primitive data treated as objects)

• Strings can be objects (or primitive data treated as objects)

• Dates are always objects

• Maths are always objects

• Regular expressions are always objects

• Arrays are always objects

• Functions are always objects

• Objects are objects

In JavaScript, all values, except primitive values, are objects.

Primitive values are: strings ("John Doe"), numbers (3.14), true, false, null, and undefined.  

Objects are Variables Containing Variables

JavaScript variables can contain single values:

var person = "John Doe";

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

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

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

A JavaScript object is a collection of named values

Object Properties

The named values, in JavaScript objects, are called properties.

PropertyValue

firstNameJohn

lastNameDoe

age50

eyeColorblue

Objects written as name value pairs are similar to:

• Associative arrays in PHP

• Dictionaries in Python

• Hash tables in C

• Hash maps in Java

• Hashes in Ruby and Perl

Object Methods

Methods are actions that can be performed on objects.

Object properties can be both primitive values, other objects, and functions.

An object method is an object property containing a function definition.

PropertyValue

firstNameJohn

lastNameDoe

age50

eyeColorblue

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

JavaScript objects are containers for named values, called properties and methods.

You will learn more about methods in the next chapters.

Creating a JavaScript Object

With JavaScript, you can define and create your own objects.

There are different ways to create new objects:

• Define and create a single object, using an object literal.

• Define and create a single object, with the keyword new.

• Define an object constructor, and then create objects of the constructed type.

In ECMAScript 5, an object can also be created with the function Object.create().

Using an Object Literal

This is the easiest way to create a JavaScript Object.

Using an object literal, you both define and create an object in one statement.

An object literal is a list of name:value pairs (like age:50) inside curly braces {}.

The following example creates a new JavaScript object with four properties:

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

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

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

Using the JavaScript Keyword new

The following example also creates a new JavaScript object with four properties:

var person = new Object();
person.firstName = "John";
person.lastName = "Doe";
person.age = 50;
person.eyeColor = "blue";

The two examples above do exactly the same. There is no need to use new Object().
For simplicity, readability and execution speed, use the first one (the object literal method).

Using an Object Constructor

The examples above are limited in many situations. They only create a single object.

Sometimes we like to have an "object type" that can be used to create many objects of one type.

The standard way to create an "object type" is to use an object constructor function:

function person(first, last, age, eye) {
    this.firstName = first;
    this.lastName = last;
    this.age = age;
    this.eyeColor = eye;
}
var myFather = new person("John", "Doe", 50, "blue");
var myMother = new person("Sally", "Rally", 48, "green");

The above function (person) is an object constructor.

Once you have an object constructor, you can create new objects of the same type:

var myFather = new person("John", "Doe", 50, "blue");
var myMother = new person("Sally", "Rally", 48, "green");