Accessing 'this' from event handler in a class

I'm trying to encapsulate some code in a class, but I can't access the 'this' object from within an event handler, since 'this' has the event target in it.

function MyClass() {
    this.foobar="hello";
    this.create=function() {
        var newSpan=document.createElement('span');
        newSpan.innerHTML='sometext';
        newSpan.onmouseup=this.SPANonmouseup;
        document.body.appendChild(newSpan);
    }
    this.SPANonmouseup=function (e) {
        alert(this.foobar);
        alert(this);
    }
}

Code (markup):

The first box reads 'undefined', the second reads '[object HTMLSpanElement]'. How can I access the class variables from an encapsulated event handler?

 

I found the solution. Declare a private variable within the class, and assign 'this' to it in the constructor. Private variables have scope in all class functions:

function MyClass() {
    [b]var t=this;[/b]
    this.foobar="hello";
    this.create=function() {
        var newSpan=document.createElement('span');
        newSpan.innerHTML='sometext';
        newSpan.onmouseup=this.SPANonmouseup;
        document.body.appendChild(newSpan);
    }
    this.SPANonmouseup=function (e) {
        alert(t.foobar);
    }
}

Code (markup):