zoltan-mihalyi/private

Private: simple class and inheritance system, with easy private member and method support!

Private

Private: simple class and inheritance system, with easy private member and method support!

• Private members
• Private methods
• Abstract methods
• Final methods
• Lots of fun

Take a look:

A = Private.class({
    getX: function(){
        return this.x;
    },
    setX: function(x){
        this.x = x;
    }
});

var a = new A();
a.setX(42);
console.log(a.x); //undefined
console.log(a.getX()); //42

Check out what you can do: https://github.com/zoltan-mihalyi/Private/blob/master/example.js

How does it work?

The main problem is to hide private members and methods. We use prototype chain to achieve this. If the private methods and members are "lower" in the prototype chain, we can't access them through a reference of "new A()" but a private method can see the public and private methods and members too. But how can the public methods access the private methods and members, like getters and setters? The key is the using of proxy methods. The object's prototype contains the proxy methods, which call the original methods with the private object as context, so each method can work with the private data, even the public ones.

                +---------+
                I Public  I Same for each object
                I proxy   I -----+
                I methods I      I
                +----^----+      I
                     I           I
           __proto__ I           I
                     I           I
                +----+----+      I
new A() ------> I Public  I      I
                I members I      I
                +----^----+      I
                     I           I
           __proto__ I           I
                     I           I
                +----+----+      I
                I Private I      I
                I members,I <----+ original methods are called with this context
                I methods I
                +---------+

How does it look like with inheritance assuming B is a superclass of A?

               +-----------+
               I Public B  I
               I proxy     I -------+ The methods of B use the private data of B as context
               I methods   I        I
               +-----^-----+        I
                     I              I
           __proto__ I              I
                     I              I
               +-----+-----+        I
               I Public A  I        I
               I proxy     I --+    I The methods of A use the private data of A as context
               I methods   I   I    I
               +-----^-----+   I    I
                     I         I    I
           __proto__ I         I    I
                     I         I    I
                +----+----+    I    I
new A() ------> I Public  I    I    I
                I members I    I    I
                +-^-----^-+    I    I
                 /       \     I    I
                /__proto__\    I    I
               /           \   I    I
         +----+----+   +----+--v-+  I
         I Private I   I Private I  I
         I data of I   I data of I  I    Different classes in the inheritance chain
         I B       I   I A       I  I    don't share their private data.
         +------^--+   +---------+  I
                I                   I
                +-------------------+