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All about Events

JavaScript’s interaction with HTML is handled through

events

that occur when the user or browser

manipulates a page. When the page loads, that’s an event. When the user clicks a button, that

click, too, is an event. Developers can use these events to execute coded responses, which cause

buttons to close windows, messages to be displayed to users, data to be validated, and virtually

any other type of response imaginable to occur.

When events first appeared in browsers (IE 3.0 and Netscape Navigator 3.0), they focused on mov-

ing some server functionality to the client. At that time, the standard method for accessing the

Internet was through a dial-up connection and modem. With speeds topping out at 56 kbps, each

trip to the server could turn into minutes of down time.

JavaScript is designed to solve this problem by allowing such functionality to take place on the

client, saving a trip to the server. As such, most of the early events centered on the use of forms

and form elements, where simple validation could be more efficiently carried out. Through the

years and browser versions, events continued to grow to support more of the page.

Events Today

As discussed earlier, events are a part of the Document Object Model (DOM). Unfortunately, as

also discussed previously, no events are defined in DOM Level 1 and only in a subset in DOM

Level 2. The full development of events occurred in DOM Level 3, which was finalized in 2004.

With few standards to guide them early on, browsers developers were left to invent their own

event models. Internet Explorer first created and implemented its own event model in version 4.0

(circa 1995) and hasn’t altered it significantly since that time. Of course, no DOM standards existed

at that point, which means Internet Explorer still uses what can be considered a proprietary event

model. Some of its design, however, was eventually folded in the DOM.

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