Comments on: How to create an object with private variables and methods

By: boiledwater

boiledwater — Thu, 29 Oct 2009 08:40:05 +0000

yes,the essential is closure!

By: How to write a singleton class in javascript | Javascript Kata

How to write a singleton class in javascript | Javascript Kata — Mon, 05 Oct 2009 14:49:03 +0000

[...] the new solution using a private variable for the [...]

By: Dan

Dan — Fri, 25 Sep 2009 21:01:20 +0000

@BK You could do it that way to. I just prefer the other notation… thanks for commenting about this way of doing things.

Keep them coming, I’ll probably write a post about how many different ways of using private variables in an object

By: BK

BK — Fri, 25 Sep 2009 20:36:48 +0000

Forgot to remove the “return” line.

Here is a simpler example:

function test(){
var rot=”a”;
this.rotted=function(){return rot};
}

var test2 = new test()
alert(test2.rot); //Returns undefined
alert(test2.rotted()); //Returns a

By: BK

BK — Fri, 25 Sep 2009 20:35:38 +0000

Oups… Forgot to remove the return line

Simpler sample:

function test(){
var rot=”a”;
this.rotted=function(){return rot};
}
var test2 = new test()
alert(test2.rot); //returns undefined
alert(test2.rotted()); //returns a

By: BK

BK — Fri, 25 Sep 2009 20:33:40 +0000

Scoping variables is one of the base OO principle: encapsulation. This is the main reason I think to do it.

Also, why not simply do

function PrivateCats() {
// This is the list of cat names
var nameList = [];

// This is a private method
var lastCat = function() {
// Note : I don’t use “this” to access private variables
// thanks to the power of closures!
return nameList[nameList.length-1];
}

// These are our public methods!
// This is where we create another scope to
// avoid external objects to use the private variables.
this.add = function(name) {
// Note : once again, I don’t use “this”
// to access the private variables and methods
nameList.push(name);
return lastCat();
},
this.names = function() {
return nameList;
}
}

Seems even more simple I think… And works the same since this isn’t in the same scope as the var declarations. Maybe I missed something… I’m starting to become rusted in JS

By: Dan

Dan — Thu, 24 Sep 2009 14:13:57 +0000

@Yansky It’s less about collisions and more about cleaner code. If all the methods of an object are public, it could be a harder for other programmer to use your code.

By: Yansky

Yansky — Thu, 24 Sep 2009 09:26:18 +0000

I don’t see the advantage to using private variables as opposed to namespacing. Sure it may be accessible outside of the function, but the fact that it’s namespaced means there wont be any problems with variable name collisions right?
e.g.

function foo(){
foo.bar={};
}

var bar={}; //no collision

By: Dan

Dan — Wed, 23 Sep 2009 18:15:14 +0000

@Topper There’s a hundred ways of assigning functions and I picked the easiest one to understand but it may be hard to read when the class grows. Sometimes, I use _privateMethod() to distinguish them easily from public methods but I’m not decided if I should really use this notation.

Anyways, thanks for your thoughts! Someone that would read the comments would see other ways to do it.

By: Topper

Topper — Wed, 23 Sep 2009 16:07:03 +0000

The only thing about specifying your scope in the return object, is that it can be confusing to read (or see where public vs private stops… this is totally just a semantic quibble but:

function PrivateCats() {
var klass = {};

var privateFunction = function () {};

klass.publicFunction = function () {};

return klass;
}

Seems to be a little easier to read.