javascript - Revealing module pattern disadvantages

Question

I recently got familiar with the Revealing Module pattern and I've read quite a few articles about it.

It seems like a very good pattern and I would like to start using it in a big project I have. In the project I'm using : Jquery, KO ,requirejs, Jquery Mobile, JayData. It seems to me like it'll be a good fit for the KO ViewModels.

In specific I'd like to use THIS version of it.

One thing I could not find are disadvantages for using this pattern, is it because there aren't any (I find it hard to believe)?

What should i consider before starting to use it?

Answer 1

The Revealing Module Pattern (RMP) creates objects that don't behave well with respect to overriding. As a consequence, objects made using the RMP don't work well as prototypes. So if you're using RMP to create objects that are going to be used in an inheritance chain, just don't. This point of view is my own, in opposition to those proponents of the Revealing Prototype Pattern.

To see the bad inheritance behavior, take the following example of a url builder:

function rmpUrlBuilder(){
  var _urlBase = "http://my.default.domain/";
  var _build = function(relUrl){
    return _urlBase + relUrl;
  };

  return {
    urlBase: _urlBase,
    build: _build
  }
}

Setting aside the question of why you would use RMP for an object with no private components, note that if you take the returned object and override urlBase with "http://stackoverflow.com", you would expect the behavior of build() to change appropriately. It doesn't, as seen in the following:

var builder = new rmpUrlBuilder();
builder.urlBase = "http://stackoverflow.com";
console.log(builder.build("/questions"); // prints "http://my.default.domain/questions" not "http://stackoverflow.com/questions"

Contrast the behavior with the following url builder implementation

function urlBuilder = function(){
  return {
    urlBase: "http://my.default.domain/".
    build: function(relUrl){ return this.urlBase + relUrl;}
  }
}

var builder = new urlBuilder();
builder.urlBase = "http://stackoverflow.com";
console.log(builder.build()); // prints "http://stackoverflow.com/questions"

which behaves correctly.

You can correct the Revealing Module Pattern's behavior by using this scope as in the following

function rmpUrlBuilder(){
  var _urlBase = "http://my.default.domain/";
  var _build = function(relUrl){
    return this.urlBase + relUrl;
  };

  return {
    urlBase: _urlBase,
    build: _build
  }
}

but that rather defeats the purpose of the Revealing Module Pattern. For more details, see my blog post http://ilinkuo.wordpress.com/2013/12/28/defining-return-object-literals-in-javascript/