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Introduction to Objects

Objects are the foundation of JavaScript.  Therefore, an understanding of objects as they relate to web development is essential to understanding JavaScript.  Everything we do with JavaScript relies on one or more objects.

An object is simply a collection of Properties, Methods and Events.  Let's use a Telephone as an example.

Objects have Properties:

You might describe an telephone by size, color, style (wall, desk, cordless or cellular, Rotary or Touch Tone.

Computer related objects such as buttons, text boxes and even the web page itself also have properties such as size, color or name, just like the telephone.  Properties are usually designated by nouns.

Objects have Methods:

Methods are what the object does.  For example, a telephone is a communications device that converts sound waves into electrical impulses that can be sent great distances.  It can also convert these electrical impulses back into sound so we can hear the message being transmitted.

Computer related objects also have methods such as open, write, close and focus.  Methods denote action and are therefore usually designated by verbs.

Objects have Events:

A telephone rings notifying you that someone wants to talk to you.  It is the up to you to decide how you will respond to this event (answer or ignore).

Computer related objects also have events such as onclick, ondblclick, onmouseover and onmouseout.  We use these events to start our script running.

When an event occurs it is referred to as firing (e.g., user clicks on button and that buttons onclick event fires), the event is sent to the operating system which in turn sends it to the appropriate software.  In this case the browser.  If the browser has been notified to listen for this event or use (capture) it, the browser will notify the scripting engine which script to run.

No matter how simple, or how complex a script is, all we ever do is work with, or manipulate and exploit, properties, methods and events of objects.