Question

Is it possible to combine this whole definition into one declaration instead of breaking it apart?

First Part

var Pan = function(){};

Second Part

Pan.prototype = {

 //private variables
 Id: null,

 //public methods
 GetId: function(){
    alert(Id);
 }
}

Answer 1

You can always do:

var Pan = function () {
    var Id = null;

    this.GetId = function(){
        alert(Id);
    }
};