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EXPLANATION ( CONTINUED )
3
A new property, called publisher, is assigned to the book1 object. It is available for
this instance of the object.
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JavaScript retrieves and displays the value of the publisher for the book1 object.
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The second book object does not have access to the publisher property. It is unde-
fined (see Figure 8.13) .
Figure 8.13 Defining a new property for an object.
8.5.1 Adding Properties with the Prototype Property
What if in the previous example book2 we want to add a publisher property so that it is
extended to all instances of the Book class? All objects have a prototype property. We can
use the Book's prototype property to assign new properties to the Book class that will now
be available to the Book class and any instances of the class; that is, all Book objects will
have the new properties. In Example 8.12, we will add new properties to the Book class.
EXAMPLE 8.12
<html>
<head><title>Object Properties</title>
<script type="text/javascript">
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function Book(title, author){
this.title =title;
this.author=author;
}
</script>
</head>
<body bgColor="#EOFFFF">
<big>
<script>
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var book1 = new Book("Kidnapped","R.L.Stevenson");
var book2 = new Book("Tale of Two Cities", "Charles Dickens")
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Book.prototype.publisher = "Penguin Books";
 
 
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