Handling Things - JavaScript

This may be news to you, but JavaScript comes with a powerfuland flexible event model, one which provides developers with astandardized way of trapping and handling client-side events likekeystrokes and mouse clicks. This two-part article takes an in-depthlook at how this event model works, demonstrating some practical (andnot-so-practical) uses of the most common event handlers.

TABLE OF CONTENTS:

By: Team Melonfire, (c) Melonfire

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June 25, 2002

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TOOLS YOU CAN USE

Unlike some other programming languages, JavaScript doesn't require you to declare and define functions before they're called. So it's possible to invoke a function via an event handler, and define that function later on in your script - as the following example demonstrates:

<html>
<head>
</head>
<body>
<a href="http://somewhere" onMouseOver="popeye()"
onMouseOut="olive()"><img name="myimage" src="normal.jpg"></a>
<script language="JavaScript">
function popeye()
{
document.myimage.src='hover.jpg';
}
function olive()
{
document.myimage.src='normal.jpg';
}
</script>
</body>
</html>

If modularizing your code into functions isn't really your cup of tea (why ever not?!), you can even have the JavaScript code accompany the event handler directly.

<html>
<head>
</head>
<body>
<a href="http://somewhere"
onMouseOver="document.myimage.src='hover.jpg'"
onMouseOut=" document.myimage.src='normal.jpg'"><img name="myimage"
src="normal.jpg"></a>
</body>
</html>

JavaScript comes with handlers for most common user events...and quite a few uncommon ones. Here's a brief list of the more important ones.

onAbort - invoked when the user aborts the loading of an image by clicking the STOP button

onClick - invoked when the user clicks the specified object

onFocus - invoked when the target object receives focus

onBlur - invoked when the target object loses focus

onMouseOver - invoked when the user passes the mouse over the target object

onMouseOut - invoked when the mouse pointer leaves the target object

onSubmit - invoked when the user clicks the Submit button in a form

onChange - invoked when the user changes the contents of a text field

onSelect - invoked when the user selects the contents of a text field

onReset - invoked when the user clicks the Reset button in a form

onLoad - invoked when the target image or document is loaded

onUnload - invoked when the target image or document is unloaded

Let's now look at these in greater detail.

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