// using Prototype.js
this.button.observe('click',this.selectRow.bindAsEventListener(this));

// using the Apply method of JavaScript
this.button.observe('click',createRef(this, function() { alert(this.num); }));

// using MS AJAX library
this.button.observe('click',Function.createDelegate(this,function() { alert(this.num); }));

// holding the reference to the current object
var self = this;

// using the JQuery library
$(this.button).bind('click',{self:this},function(event)
{
var that = event.data.self;
alert(that.num);

});