Recently i saw the following code that creates a class in javascript:

var Model.Foo = function(){
  // private stuff
  var a, b;

  // public properties
  this.attr1 = '';
  this.attr2 = '';

  if(Model.Foo._init === 'undefined'){
    Model.Foo.prototype = {
      func1 : function(){ //...},
      func2 : function(){ //... },
      //other prototype functions
    }
  }
  Model.Foo._init = true;
}

// Instantiate and use the class as follows:
var foo = new Model.Foo(); foo.func1();

I guess the _init variable is used to make sure we don't define the prototypes again. Also, i feel the code is more readable since i am placing everything in a function block (so in oop-speak, all attributes and methods are in one place). Do you see any issues with the code above? Any pitfalls of using this pattern if i need to create lots of classes in a big project?