var myButton = Ext.extend(Ext.Button, {
	text: 'Click me',
	initComponent: function() {
		var application = this.application;
		this.handler = function(e){
			var myVariable = 'This is a variable';
			application.fireEvent('myCustomEvent', myVariable);
		}
                myButton.superclass.initComponent.call(this);
	}
});