ObjectA.prototype = new MVCObject();
var object_a = new ObjectA();

ObjectA.prototype.foo_changed = function()
{
console.log('ObjectA foo changed, it is now: ' + this.get('foo'));
};

//  Not working Hook
object_a.changed('foo', () => {
console.log('===> index.js ===> Need to be Fired');
})

$(function(){

$('#btn-panel').click(function(){

    object_a.set('foo', 'I am cool');
});
});

object_a.on('foo_changed', function() {
      console.log('===> index.js ===> First Listener');
})

object_a.on('foo_changed', function() {
      console.log('===> index.js ===> Second Listener');
})