Netscape 4 and Netscape 6 event models
Tutorial written and contributed by Jason Davis, moderator of
the JK Forum.
Edited/ minor additions by JK.
Please see tutorial footnote for additional/bio info on author.
This tutorial looks at the now legacy event model of Netscape 4, and
more applicable, that of Netscape 6 as well (Firefox shares a very similar
event model as NS6's). Many developers struggle with Netscape 4 and 6's seemingly lacking event model,
where there is no explicit event object to work with. In IE, there is
window.event, which provides detailed information regarding the
occurring event (ie: where the mouse was, what element was clicked on
etc). Well, there are in fact ways to compensate for the lack of this
"miracle object" in Netscape, and in this tutorial, we'll see how!
 Netscape 4+ does support
window.event
(well, indirectly)!
Let's look at the simple example of embedding an event handler inside a
link:
<a href="file.html" onclick="doSomething()">
inside doSomething(), you can get the event info in IE via
window.event, but what many don't
realize is you can accomplish the equivalent in NS. Netscape places event
handler functions into a wrapper function, and passes the event object as
an argument to it. So, how do we get to it?
#1: Explicitly passing an "event" parameter
We can allow functions attached to an event in Netscape to access the
event object by passing in event as a parameter. For example:
<a href="file.html" onclick="doSomething(event)">
event is a variable in the onclick() function namespace, or scope.
doSomething() is inside that scope as well, so we pass the object event
into it. Then you can reference event inside doSomething().
#2: By invoking arguments.callee.caller.arguments[0]
So far so good, but what if you don't want to use any event argument,
as you want to pass your own argument without messing it up in Internet
Explorer?
In JavaScript1.2+, the code
arguments.callee.caller
allows you to reference the containing wrapper function, which the event
object is passed into. By taking advantage of this fact, we can rewrite
doSomething() to retrieve the event object in Netscape directly inside the
function:
function doSomething() {
// arguments.callee.caller.arguments[0] references the event object
alert(arguments.callee.caller.arguments[0].type) // "click"
}
Voila, we got the event without passing a single argument, now, cross
browser:
function doSomething() {
var theEvent=window.event || arguments.callee.caller.arguments[0];
// rest of script
}
Pretty cool uh?
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