Objects - JavaScript by Example - page 200

lookup chain, can continue until JavaScript reaches the top of the chain. You might
recall that the top object is called the Object object and it too has a prototype .
Example 8.13 uses the prototype for the Object object and the prototype for the Book
object to create new properties. To retrieve a property for a Book object, JavaScript
would look up the property in the following order:

1. The object itself
2. The Book.prototype
3. The Object.prototype

First JavaScript starts with a Book object. If looking for the Book's title and author ,
then there is no need to look further; if, on the other hand, we want to get the publisher
or category , then JavaScript will go up the chain and look at the Book's prototype, and
finally, if not there, go to the top Object object and look there (see Figure 8.15). If the
Object object has not defined the property, it is undefined . (Much of the information in
this paragraph should be credited to a paper on objects written by Mike Koss at
http://mckoss.com/jscript/object.htm. )

Constructors Prototype Chain

Object

Object.prototype.category

function
Book()

Book.prototype.publisher

book1 book2

book1.author book2.author

book1.title book2.title

Figure 8.15 JavaScript looks for the property with Example 8.13.