Using prototype JavaScript - best practice

Question

Currently I am working in a project where we are writing Object Oriented JavaScript. In this project I have seen two different ways of defining a class:

1: Declare functions at once on the prototype

My.Namespace.ClassName = function(param1, param2) {
   this.member1 = param1;
   this.member2 = param2;
};

My.Namespace.ClassName.prototype = {
   myFunction1: function() {
      return this.member1 + " " + this.member2;
   },

   myFunction2: function(param1) {
      this.member3 = paraml;
   }
};

2:Prepare each function individual on the prototype

My.Namespace.ClassName = function(param1, param2) {
   this.member1 = param1;
   this.member2 = param2;
};

My.Namespace.ClassName.prototype.myFunction1 = function() {
   return this.member1 + " " + this.member2;
};

My.Namespace.ClassName.prototype.myFunction2 = function(param1) {
   this.member3 = paraml;
};

Is there any difference in how JavaScript behaves based on the two given examples or is it only a style difference?

Personally I haven't seen any behavior difference but I have the feeling that there must be a subtle difference which I am currently missing.

Besides that. I would like to know whether this is a common practice or are there much better ways to define classes.

Answer 1

There is a subtle difference. In the first method, when you overwrite the prototype, there was a property there that is now lost. That's the constructor, which points back to your function. The constructor allows you to recreate the type of object that it is.

You can easily get it back and so use the first method by manually setting it:

My.Namespace.ClassName.prototype = {
   myFunction1: function() {
      return this.member1 + " " + this.member2;
   },

   myFunction2: function(param1) {
      this.member3 = paraml;
   },
   constructor: My.Namespace.ClassName
};

See also: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/constructor