JavaScript 2.0-The Complete Reference, Second ... - freecodingtutorial

The objects in JavaScript are summarized in Table 6-1.
Table 6-1: The Four Types of Objects Available to JavaScript
Type Example Implementation
Provided By
User-defined Programmerdefined
Customer
or Circle
Programmer None
Built-in Array, Math The browser via
its JavaScript
engine
Governing
Standard
ECMA-262
Browser Window, Navigator The browser None (though
some portions
adhere to an ad
hoc standard)
Document Image,
HTMLInputElement
The browser via
its DOM engine
W3C DOM
There is some overlap in these four categories. For example, before the advent of the official
DOM standard, objects such as Image were browser objects because each vendor
implemented their own feature set. The major reason there is such overlap is that there is no
one standard governing how all aspects of JavaScript are supposed to behave. The ECMA-262
standard governs the nuts and bolts of the language itself. The W3C‘s DOM specification
dictates how structured documents like Web pages should be presented to a scripting
environment. Browser vendors define access to the user interface as they see fit and even
create their own proprietary extensions to the DOM. The result is a chaotic and somewhat
confusing set of technologies that come together under the umbrella of ―JavaScript.‖
The good news is that browser vendors have finally settled on a de facto standard for browser
objects. This ―standard‖ is more an artifact of historical circumstances and browser wars than
the product of a rational design process. This is evidenced by the fact that the Navigator object
is supported by Opera, Netscape, and Internet Explorer despite obviously deriving its name
from Netscape‘s original Navigator browser. While the features implemented by Navigator
objects are somewhat consistent across browsers, a close examination reveals some variation
in the support of its properties by the different browser types and versions.
This chapter covers the fundamental ways that objects behave and can be manipulated in
JavaScript. The specific capabilities of built-in, browser, and document objects are discussed in
detail in chapters that follow.
Object Fundamentals
An object is an unordered collection of data, including primitive types, functions, and even other
objects. The utility of objects is that they gather all the data and logic necessary for a particular
task in one place. A String object stores textual data and provides many of the functions you
need to operate upon it. While objects aren‘t strictly necessary in a programming language (for
example, C has no objects), they definitely make a language that contains them easier to use.
Object Creation
An object is created with a constructor, a special type of function that prepares a new object for
use by initializing the memory it takes up. In Chapter 4, we saw how objects are created by
applying the new operator to their constructors. This operator causes the constructor to which it
is applied to create a brand-new object, and the nature of the object that is created is
determined by the particular constructor that is invoked. For example, the String() constructor