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Javascript Object

Updated on November 2, 2007

An object is a collection of properties. These properties can either be primitive data types, other objects, or functions (which in this case are called methods, but more on this later).

A constructor function (or simply, constructor) is a function used to create an object - this too we'll discuss in detail later.

Javascript comes with many built-in objects, such as the Array, Image and Date objects.

For instance

var Image1 = new Image();

Image1.src = "myDog.gif";

creates a new Image object, and assign a property to the new Image object: the src property. Image1 is a new Image object (an instance of the Image object).

Creating an object in Javascript

//myObject function is a constructor

function myObject(){


var myObjectVar = new myObject();

alert(typeof myObjectVar); // displays "object"

The new keyword tells JavaScript to create an object following the blueprint set forth in the myObject() constructor function.

this special variable

Every object method has a variable -

this - which refers to the current instance of that object from which the method is called.

Creating a Property

function myObject(initialvalue){

this.myProperty = initialvalue;


var myObjectVar = new myObject("This is a Property");

alert(myObject.myProperty); // displays "This is a Property"

Creating a method

function myMethod(message) {



function myObject(initialvalue){

this.myProperty = initialvalue;



var myObjectVar = new myObject("This is a Property");

alert(myObject.myMthod("This is a method")); // displays "This is a Method"


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