Problem using object methods as event handlers

#1 November 4th, 2005, 12:05 AM

Hello all.

I've a bit of a problem. I would like to use a method in an object as an
event handler. Unfortunately, when the method is called the "this" object
references the event trigger rather than my object.

For example, with the following code, an alert will be shown when the page
loads
where the value of my_name is "My Object" and nodeName is 'undefined".
Dismissing
that alert and then clicking anywhere on the page will present another alert
where the
value of my_name is "undefined" and the value of nodeName is "BODY".

<html>
<head>
<title>Event Example</title>
<script type="text/javascript" language="JavaScript">
function x( n )
{
this.my_name = n;
}
x.prototype.toString = function( level ){ return "ABC"; }
x.prototype.event_handler = function( e )
{
var evt = ( e ? e : ( window.event ? window.event : null ));
if( !evt ) return;
alert( "x.event_handler()\n" +
" my_name:\t" + this.my_name + "\n" +
" nodeName:\t" + this.nodeName + "\n" +
" event:\t\t" + evt.type );
}

function body_onload()
{
my_obj = new x( "My Object" );
my_obj.event_handler( { type:'Dummy' } );
document.body.onclick = my_obj.event_handler;
}
</script>
</head>
<body onload="body_onload();">
<input id="Button1" name="Button1" type="button" value="Button 1">
</body>
</html>

Any suggestions as to how to get around this?

Thanks in advance.,

Dave

#2 November 4th, 2005, 01:47 AM

D. Patterson wrote:[color=blue]
> I've a bit of a problem. I would like to use a method in an object as
> an event handler.[/color]

Not at all an unusual desire.
[color=blue]
> Unfortunately, when the method is called the "this"
> object references the event trigger rather than my object.[/color]
<snip>

There are a number of techniques that handle this problem. As you are
assigning the handlers as a function reference the most appropriate
method is described here:-

<URL: http://www.jibbering.com/faq/faq_notes/closures.html >

Richard.

#3 November 4th, 2005, 02:15 PM

Wow. Great article.
Now I go play for a while.
I'll post the results....later.

Thanks
Dave

"Richard Cornford" <Richard@litotes.demon.co.uk> wrote in message
news:dkeh53$kbv$1$8300dec7@news.demon.co.uk...[color=blue]
> D. Patterson wrote:[color=green]
> > I've a bit of a problem. I would like to use a method in an object as
> > an event handler.[/color]
>
> Not at all an unusual desire.
>[color=green]
> > Unfortunately, when the method is called the "this"
> > object references the event trigger rather than my object.[/color]
> <snip>
>
> There are a number of techniques that handle this problem. As you are
> assigning the handlers as a function reference the most appropriate
> method is described here:-
>
> <URL: http://www.jibbering.com/faq/faq_notes/closures.html >
>
> Richard.
>
>[/color]

Problem using object methods as event handlers

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