JavaScript Callback Scope

function foo(id) {
    this.dom = document.getElementById(id);
    this.bar = 5;
    var self = this;
    this.dom.addEventListener("click", self.onclick, false);
}

foo.prototype = {
    onclick : function() {
        this.bar = 7;
    }
};

var x = new foo('test');

this.dom.addEventListener("click", self.onclick, false);

this.dom.addEventListener(
  "click",
  function(event) {self.onclick(event)},
  false);

function bind(scope, fn) {
    return function () {
    	fn.apply(scope, arguments);
    };
}

this.dom.addEventListener("click", bind(this, this.onclick), false)

this.dom.addEventListener("click", function(event) {
    self.onclick(event)
}, false);

var obj = ...;
function callback(){ return obj.method() };
something.bind(callback);