Private and privileged methods vs prototype methods

Question

In JavaScript I can create private and privileged methods by declaring them in the constructor. By this I have to move them out of the prototype of the object. Then I lose the possibility of inheritance and some performance since every object will have it's own copy of those methods instead of accessing one prototype object.

So my question now is what might be a petter pattern: Make use of private and privileged methods or not. I am no big fan of dangling so I want to avoid this. So what to do?

What are your experiences?

Answer 1

I've never seen any value in creating so-called 'private' functions in JavaScript. Just mark them somehow to indicate that they're not part of your public API, and so API clients aren't guaranteed that the function will exist, or have the same implementation in a future version.

Apart from API consistency, there's no reason not to let people just use your private functions if they want to. Sure, it allows co-existing scripts to fuddle with your private functions, but those scripts could've already overridden your public API functions, anyway.

The accepted answer to this question has good commentary on this: Private functions in namespaced javascript

Answer 2

Convention would be to scope what is needed out... and for psuedo private or protected members to prefix your methods or properties with an underscore.

I prefer a psuedo private/protected scope...

var MyObject = (function(){
  var interalStaticVar;

  function ctor(arg1, arg2) {
    //create psuedo-protected context
    this._ = {};

    //create a psuedo-private context
    this.__ = {};

    //stash someval
    this.__.someVal = "hands off";
  }

  ctor.prototype.getSomethingPrivate = function() {
    return this.__.someVal;
  }

  ctor.prototype._doSomethingProtected = function(){ ... }

  ctor.prototype.__doSomethingPrivate = function() { ... }

  return ctor;
}());

I will say that trying to apply OO-style inheritance paradigms to JavaScript is asking for trouble and probably means you're doing something wrong. I tend to follow more SOLID designs embracing the functional event driven nature of JS in the browser.