HTML and CSS Reference
In-Depth Information
Like any other object, you can assign properties and methods to the prototype object.
You do this with the prototype property. When values are assigned to an object's proto-
type property, they are automatically extended to all instances of the class. After an
object has been created, new properties and methods can be added to the
prototype
object, and any objects created after that will automatically inherit the new properties
and methods. This is how JavaScript implements inheritance. It allows you to reuse code
and customize an object.
Let's say we define a constructor function called
Book()
with a set of properties such
as
title
and
author
. The
Book()
constructor function is JavaScript's way of creating a class.
The constructor function is called with the
new
keyword and creates an instance of the
Book class, an object called
book1
, and then the constructor function is called again and
creates another Book object called
book2
, and so on. Now, after creating
book1
, we add
another property such as
book1.publisher
. This property affects
book1
, and only
book1
.
The
publisher
property is not extended to
book2
. The property would have to be added
separately to each Book object that needs it or by adding it to the Topic's prototype.
Adding a new property without using the prototype property
EXAMPLE
8.11
</html>
<head><title>Object Properties</title>
1
<script type="text/javascript">
function Book(title, author){
this.title =title;
this.author=author;
}
</script>
</head>
<body bgColor="#EOFFFF">
<big>
<script>
2
var book1 = new Book("Kidnapped","R.L.Stevenson");
var book2 = new Book("Tale of Two Cities", "Charles Dickens")
3
book1.publisher="Penguin Books";
document.write(book1.title + " is published by "+
4
book1.publisher
+ "<br />");
document.write(book2.title + " is published by " +
5
book2.publisher
); //
Doesn't have this property
</script>
</big>
</body>
</html>
EXPLANATION
1
The constructor function called
Book
will define the properties and methods for
a
Book
class. The function takes two parameters.
2
Two new Book objects are created,
book1
and
book2
.
Continues
