Creating Objects

By: aathishankaran Printer Friendly Format    

Most of the time you will be referencing objects, which are built-in to the DOM.

However, you may want to create your own objects for storing data within a JavaScript program. There are several ways to create a new object, but we'll look at two: creating a direct instance of an object and creating an object prototype. 

direct instance of an object 

Despite the awkward sound name, a "direct instance of an object" simply means creating a new single object, such as myPetDog: 

myPetDog=new Object () ;

myPetDog.name="Barney";

myPetDog.breed="beagle";

mypetDog.year=1981; 

Assigning a method to your new object is also simple. Assume that you already have coded a function named woof0, which causes a barking sound to play: 

myPetDog.woof=woof; 

Prototype of an object 

Sometimes, you'll want to create a "template" or prototype of an object. This does not create an actual instance of the object, but defines the structure of the object. In the future, then, you can quickly stamp out a particular instance of the object. Suppose that instead of myPetDog, you created a prototype object named petDog. This object could then be a template for a particular pet dog object. First, create a function which defines the petDog structure: 

function petDog(name, breed, year)

{

this. name = name;

.this. breed = breed;

this. year = year;

} 

Now that the petDog prototype has been set, you can quickly create single instances of a new object based on the petDog structure: 

myPetDog=new petDog(“barney","beagle",1981);

yourPetDog=new petDog(“max","terrier",1990); 

Example:

<Html>

<Head>

<Title>User Defined Objects</Title>

<Script>

 

function Print ()

{

document.write (“Employee Number: “+this.Eno);

document.write ("<br>") ;

document.write ("Employee Name: "+this. Ename) ;

document.write ("<br>");

document.write ("Employee Salary: “+this. Salary) ;

}

function Hra ()

{

document.write ("<br>") ;

document.write("HRA: "+(this.Salary*SO/lOO»;

document.write("<br>");

}

 

function Employee(Eno,Ename,Salary)

{

this.Eno=Eno;

this.Ename=Ename;

this.Salary=Salary;

 

this.Hra=Hra;

this.Print=Print;

}

</ Script>

</Head>

<Body bgcolor=#c0c0c0>

<Script>

var emp0l=new Employee(l00,"aathishankaran”,90000);

emp0l. Print ( ) ;

emp0l. Hra( ) ;

</ Script>

</Body>

</Html> 

Output 

Employee Number : 100

Employee Name : aathishankaran

Employee Salary : 90000

HRA : 45000





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