Attach a class method to event handler

Hi guys,

until now I make so:

[html]
<div id="my_div"><!-- content --></div>

[simple-js]
MyClass.prototype.doSomething = function( ) {};
MyClass.prototype.assignFun = function( )
{
var selfObj = this;
document.getElementById('my_div').onclick = function ( e )
{
selfObj.doSomethingWith( e || event );
}
}

How do I avoid the closure of my object reference?
And MyClass is not a Singleton...