Question

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(typeof 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?

Answer 1

It just seems unnecessarily complex. You need to be disciplined to not use any parameters or local variables of Model.Foo in the implementation of the prototype extension. Its odd to overwrite the entire .prototype object and not just add individual members as well. Why not just do this the normal way?

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

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

Model.Foo.prototype.func1 = function(){ //...};
Model.Foo.prototype.func2 = function(){ //... };

alternate allowing per-instance member variables private

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

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

  this.func1 = function(){ //...};
  this.func2 = function(){ //... };
}