I understand what you are saying, This was mainly meant as an introduction/execrcise for people coming from other languages, although in reality there’s no exact mapping.

Sorry for a late reply!
And thanks, I’m glad that you like my articles on JavaScript!

Adam’s example does indeed work and allows the desired access. The downside of it, though, is that it will affect performance. For any method of an object that you will create several instances of, you would want to have those methods on the prototype instead.

I am new at Javascript (but learning hard). Your articles are really nice.

Regarding the solution posted above by Adam Silver, I cannot see anything wrong with it; he is creating MyClass prototype from another (anonymous) object (thus making a copy the getPrivate() function). Once he has fed MyClass prototype, I cannot see why each MyClass instance needs its own copy of getPrivate(). On the contrary, I think all instances share the same getPrivate() function; in fact, MyClass constructor is an empty function, so there is no chance to redefine a new getPrivate() function each time you create a new MyClass instance.
It is true that all instances share the same privateVar as well, but this is something (as you have posted elsewhere) that cannot be resolved by the language (outside the constructor, I mean).

So, from my point of view, Adam’s approach is fully correct.

If I am wrong, explain it to me please (with some illustrative examples if you are so kind).

Thank you in advance.

Yeah, basically. A privileged method can access private members, whereas, in more regular languages, public methods can’t really do that.

I can’t see any difference in the syntax for a privileged method and a public method (when not using prototype) so… is a method called public/privileged based on the variables it access?

Thanks in advance

JT.

Glad that you liked it!

Thanks!!

Well, they’re shared by instances, so-to-say, but not by prototype methods, and that’s what Adam was aiming for.

Also, good posting the link, it’s good to have in this context!

Kind Regards

I think I will write one, in some form at least.

Ah, I see what you mean. That does indeed work.
The problem with it, however, is that the prototype for MyClass becomes an anonymously created object, where you declare the public method getPrivate inline in the constructor, instead of using a prototype.

I.e. each instance would have to create its own getPrivate method, instead of using the one inherited down through the prototype chain.

Can you not do the following:


var MyClass = function() {
}
MyClass.prototype = new(function(){
var privateVar = 1;

this.getPrivate = getPrivate;
});
var myInstance = new MyClass();
alert(myInstance.getPrivate()); // this alerts 1


I just tested and it seemed to work.

Interesting thinking!
The problem, however, with that approach is that you can’t access that private variable in any other method for the object. I.e., this won’t work:


MyClass.prototype.getPrivate = function(){
return myPrivateMember;
};

With Andrea’s solution above, it is possible with private variables accessible to all methods, as long as they’re declared within the closure, but outside the constructor.

Maybe I should write a post explaining what Andrea touched on above, with private members, to have it more easy to overview than in the comments.

With regards to using private methods and variable on the prototype, I believe you can do the following:

var MyClass = function() {
}

MyClass.prototype = new (function(){
this.myPublicMember = "public";
var myPrivateMember = "private";
});


I would love to see a post on using the prototype in much more detail.

Thanks

Yeah, exactly my thinking.

Thank you! It passed my mind while writing to Andrew, but naturally, a closure with the constructor (and returning the constructor as well) together with private members is a possible approach.

The only downside, structure-wise, from that is that you can’t define anything private in the actual constructor, and access from somewhere else.