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An object is a "package” of data; a collection of properties
(variables) and methods (functions) all classed under a single name. For
example, imagine that there was an object named car. We could say that the car
object possesses several properties: make, model, year, and color, for example.
We might even say that car possesses some methods: go(), stop(), and reverse().
Although car is obviously fictional, you can see' that its properties and
methods all relate to a common theme.
own objects for storing data. More commonly, though, you will use the many
"built-in” objects which allow you to work with, manipulate, and access
the Web page and Web browser. This set of pre-existing objects is known as the
"Document Object Model".
Often referred to as the DOM, this
of these objects are directly related to characteristics of the Web page or
browser. The reason we qualify the term "built in” is because the DOM is
specification, standardized by the ECMA, does not actually specify the nature or
specifics of the DOM. Consequently, Netscape and Microsoft have developed their
own individual DOM's which are not entirely compatible. Additionally, the DOM
scripting languages as well.
Below is a graphical chart
illustrating a high-level view of Netscape's DOM. Microsoft's DOM is actually a
superset of Netscape's, and so the chart below actually represents a subset of
Microsoft's own DOM.
Access the properties of an object
with a simple notation: objectName.propertyName. Both the object name and
property name are case sensitive, so watch your typing. Because a property is
essentially a variable, you can create new properties by simply assigning it a
value. Assuming, for instance, that carObj already exists (we'll learn to create
a new object shortly), you can give it properties named make, model, and year as
an array. If you're familiar with other languages you probably recognize an
array as a collection of values residing within a single named data structure.
You can access an object's properties either using the objectName.propertyName
syntax illustrated above, or by using an array syntax:
Unlike a basic data array, an
object can also contain functions, which are known as methods when part of an
object. You call a method using the basic syntax: objectName.methodName(). Any
arguments required for the method are passed between the parentheses, just like
a normal function call.
For example, the window object possesses a method named
close (), which simply closes the specified browser window:
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