hail object literals in JS. :) Beside using it in namespace containers, I find it also very handy for emulating static objects and other contructs.

It is definitely one of the good stuff in JS and i like how you use it. Good work!

Private variables are useful in one other situation: When you're extending existing functions to do something additional. Example:

function somefunc() { ... };

(function() {
  var old = somefunc;
  somefunc = function() {
    alert('before somefunc');
    old.apply(this, arguments);
    alert('after somefunc');
})();

This prevents global namespace pollution with all kinds of 'old' function aliases.

I use private variables/methods pretty often to hide functionality that the user doesn't need to touch. However, for libraries that might be extended and need to access private variables, I provide an "expose" method that sets references to all private variables and methods in the current context. This might defeat the purpose of having private variables at all, but at the very least, it forces the person to have some idea what their doing before they can access them.

@Jonathan

Well, I've only used that in one particular case so far...

I wrote an ActiveRecord-inspired extensible database system in JavaScript. It has a layering mechanism where any method (whether public or private) can have preprocessors and postprocessors attached to it in order to add additional functionality in which case the attached functionality would need access to all internal data.

Specifically what I'm using it for is that the base database library is fairly slim, only containing enough logic to be functional. On top of this, I have a separate validation module that will attach itself to every appropriate method in the library that adds data validation primarily but could also be used to add something like constraint management. The validation module needs to add validation steps to internal/private methods as well as potentially look at the primary/foreign keys stored within the raw data so I needed the ability to expose it when necessary. Another example is that I have an unfinished SQL query module for it that needs to be able to access the raw data in order to return its result set.

I don't want to expose raw data such as the primary/foreign key indexes or data tables unless they're needed because if someone doesn't know what they're doing they can corrupt the entire database.

Anyways...you're right, I don't *need* to go private, its just an added measure to maintain data integrity. Data integrity alone can be enough to make it worthwhile, although its probably overkill in most cases.

One place where the Yahoo! guys use this technique is in the YAHOO.util.Anim class. There is a private variable called isAnimated. It's a variable that you just don't want users messing with. It only serves to inform the AnimMgr object. It has an accessor method but that's it.

If the variable were public, and the user decided to set it to false while an animation was running, the animation would remain in the AnimMgr queue, forcing the AnimMgr to loop over it on every frame of the animation, but actually doing nothing. Then, when you wanted to start the animation going again, you would have to set the boolean to true and then manually restart the AnimMgr. So it's messy, and it's a two step process later on to restart the thing.

In my opinion, this is the perfect case for a private variable. It's just not a good idea to touch the thing!

@Jonathan: Excellent point. On a second read, I realize that my comment was a bit off topic, and I tend to agree with your points.

Your code example can be made even clearer by returning the object containing the public properties and functions rather than storing it in the "obj" variable:

MyObject = function(){

  var privateMethod = function(){ /* do stuff */ };

  return {
    publicProperty:5,
    publicMethod:function(){ /* do stuff */ };
  };
}(); // run it right away

Any downsides to this?

Jonathan, could you elaborate more about your calendar example in 'code'?
How do you mean:

"The great thing about this was that each of the calendars could basically talk to each other while still having access to some core common values like what the currently selected day, month and year was."

I'd like to see how you approached this.

I was not looking for the code itself :), I am only interested in the structure of the code => 3 objects in the same namespace, accessing common values.
Would you do it like this:

if (typeof(MyNamespace) == 'undefined') var MyNamespace = {};

MyNamespace.MyObject1 = function() {
  var util = {
    _getValue: function() { return MyNamespace.value; },
    _setValue: function(value) { MyNamespace.value = value; }
  }

  var obj = {
    init: function() {},
    getValue: function() { return util._getValue(); },
    setValue: function(value) { util._setValue(value); }
  }

  obj.util = util;
  return obj;
}();

MyNamespace.MyObject2 = function() {
  var util = {
    _getValue: function() { return MyNamespace.value; },
    _setValue: function(value) { MyNamespace.value = value; }
  }

  var obj = {
    init: function() {},
    getValue: function() { return util._getValue(); },
    setValue: function(value) { util._setValue(value); }
  }

  obj.util = util;
  return obj;
}();

// set currentValue via MyObject1
MyNamespace.MyObject1.setValue('test1');

// retrieve currentValue via different objects
alert(MyNamespace.MyObject1.getValue());
alert(MyNamespace.MyObject2.getValue());

Both alert's will return 'test1'.
Any thoughts?

How would one go about setting the 'publicProperty' in the sub-module pattern from another method in the object.

for example:

MyObject = function(){
  var util = {
    privateMethod: function(){ 

       obj.publicProperty = 10;  // <- Is this possible?
    };
  }

  var obj = {
    publicProperty:5,
    publicMethod:function(){ util.privateMethod(); };
  }

  // do my object attachment
  obj.util = util;
  return obj;
}(); // run it right away

Thanks very much, been reading your posts since 2002...

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У меня кот Барс (балбес еще тот)
Кошка Мусёна