OOP in Javascript... Don't be fooled.

In JavaScript, "new" does not mean you get a clean instance of a class. class properties still have a link reference to the prototype. Here is an example of the problem.

  //example class
  var testClass = function(){};
  //class definition
  testClass.prototype = { arr: [], obj: {} };
 
  /*
   * This example shows how instance 2
   * indirectly gets instance1's array
   */
 
  //new instance 1
  var instance1 = new testClass();
  //push some stuff in the array
  instance1.arr.push('this is data 1 for instance 1');
  instance1.arr.push('this is data 2 for instance 1');
  instance1.arr.push('this is data 3 for instance 1');
 
  //new instance 2
  var instance2 = new testClass();

  //instance2 has instance1's array!
  alert(instance2.arr);
 
 
  /*
   * This example shows how instance 1
   * indirectly gets instance2's object
   */
  //put some stuff in instance2's obj
  instance2.obj['one'] = 'this is data 1 for instance 2';
  instance2.obj['two'] = 'this is data 2 for instance 2';
  instance2.obj['three'] = 'this is data 3 for instance 2';
 
  //instance1's obj was changed to instance2's obj!
  alert(instance1.obj.one + ' ' + instance1.obj.two + ' ' +  instance1.obj.three);

The solution that works is using Object.clone(new testClass) after instantiation, however not very optimal. So in the end I made sure in my constructor class, I manually reset arr and obj (this.arr = []; this.obj = {}). It's important that if you use "new testClass" you are not making a real instantiation, it's more like a simulated one. Plan on manually resetting array and object properties in your constructor so this won't happen to you!