↑
Main Page

Internet Explorer

Using this method of assignment, the event handler name must be represented in all lowercase letters to

properly respond to the event.

To assign an event handler in HTML, you simply add an event handler attribute to the HTML tag and

include the appropriate script as the attribute value, like so:

With this method, the event handler can have any case, so

onclick

is equal to

onClick

OnClick

, and

ONCLICK

. (However, if you are using valid XHTML code, event handlers should be defined using all

lowercase letters.)

When you are assigning event handlers in HTML, remember that the code contained in the attribute

value (between the quotes) is wrapped in an anonymous function, so the HTML code actually executes

the following JavaScript:

oDiv.onclick = function () {

alert(“I was clicked”);

};

Look familiar? Yes, it is the same code as the JavaScript example.

These methods both work in all modern browsers, but additional methods can make more than one

event handler per event available. Once again, Internet Explorer contains a proprietary method whereas

the DOM prescribes another.

Internet Explorer

In IE, every element and

window

object has two methods:

attachEvent()

and

detachEvent()

. As the

names indicates,

attachEvent()

is used to attach an event handler to an event and

detachEvent()

used to detach an event handler. Each method takes two arguments: the name of the event handler to

assign to (for example:

onclick

) and a function.

[Object].

attachEvent(“name_of_event_handler”, fnHandler);

[Object].

detachEvent(“name_of_event_handler”, fnHandler);

In the case of

attachEvent()

, the function is added as an event handler; for

detachEvent()

, it looks

for the given function in the event handler list and removes it. For example:

var fnClick = function () {

alert(“Clicked!”);

};

var oDiv = document.getElementById(“div”);

oDiv.attachEvent(“onclick”, fnClick); //add the event handler

//do some other stuff here

oDiv.detachEvent(“onclick”, fnClick); //remove the event handler

267

All about Events

12_579088 ch09.qxd 3/28/05 11:39 AM Page 267