Question

I want to be able to pass one object to another, then set up events that execute different methods from the initial object.

var TEST = {}; 
//User-created object
TEST.testObj = function () { this.initialize.apply(this, arguments); };
TEST.testObj.prototype = {
    initialize: function(a) {   
        this.a = a;
    },
    sayHi: function() {
    alert(a);
}
} 
//Menu accosiated with that class of objects 
TEST.testMenu = function () { this.initialize.apply(this, arguments); };
TEST.testMenu.prototype = {
    initialize: function(obj) {
        this.obj = obj;
        var menuItem = document.createElement('div');
        menuItem.innerHTML = 'Say Hi!';
        menuItem.onclick = this.obj.sayHi;
        document.body.appendChild(menuItem);
    }
}

t1 = new TEST.testObj('Test Object');
menu = new TEST.testMenu(t1);

Activating the event by clicking the div alerts undefined. It looks like it’s calling the function sayHi, but a generic one not associated with an instantiated object.

Thanks!

Answer 1

You don’t have a sayHi() function declared in this code. Just add this line

TEST.testObj.prototype.sayHi = function() {alert('hi')}

after the TEST.testObj.prototype... part. This will create a new function in TEST’s prototype chain that you can call inside the testMenu object

EDIT
The way you are binding the onclick event, this was referring to the div HTML element, not the object. This is the changed code that should work:

var TEST = {}; 
        //User-created object
        TEST.testObj = function () { this.initialize.apply(this, arguments); };
        TEST.testObj.prototype = {
            a: null, 
            initialize: function(a) {
                this.a = a;
            },
            sayHi: function() {
            alert(this.a);
        }
        } 
        //Menu accosiated with that class of objects 
        TEST.testMenu = function () { this.initialize.apply(this, arguments); };
        TEST.testMenu.prototype = {
            initialize: function(obj) {
                this.obj = obj;
                var menuItem = document.createElement('div');
                menuItem.innerHTML = 'Say Hi!';
                menuItem.onclick = function() { obj.sayHi(); }
                document.body.appendChild(menuItem);
            }
        }

        t1 = new TEST.testObj('Test Object');
        menu = new TEST.testMenu(t1);