How to access private attributes inside an inherited method in JavaScript

Question

I am trying to call a inherited method that must access private attributes from current object. But it only access the public ones, what is wrong?

My test code should alert both vars:

            function ParentClass(){
                //Priviliged method to show just attributes
                this.priviligedMethod = function(){
                    for( var attr in this ){
                        if( typeof(this[ attr ]) !== 'function' ){
                            alert("Attribute: " + this[ attr ]);
                        }
                    }
                };
            }

            function ChildClass(){
                // Call the parent constructor  
                ParentClass.call(this);

                var privateVar = "PRIVATE VAR";
                this.publicVAR = "PUBLIC VAR";
            }
            // inherit from parent class 
            ChildClass.prototype = new ParentClass();  
            // correct the constructor pointer because it points to parent class   
            ChildClass.prototype.constructor = ChildClass;

            var objChild = new ChildClass();

            objChild.priviligedMethod();

The jsfiddle version: http://jsfiddle.net/gws5s/6/

Thanks in advance, Arthur

driangle · Accepted Answer · 2012-02-06 19:02:15Z

1

Nothing is wrong. When you use the var keyword, javascript will make that variable limited to the current scope it is currently defined in.

so:

var privateVar = "PRIVATE VAR";

will only be visible from inside the block it is defined, namely ChildClass()

Check out this article for a more in-depth explanation.

edited Feb 6, 2012 at 19:02

answered Feb 6, 2012 at 18:08

driangle

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2 Comments

user1192922 Over a year ago

ok, but when a inherit the ParentClass the priviligedMethod it is inherited too, so calling it from the ChildClass the scope should be the same that i declared the privateVar. In the same scope it must be accessable, or not?

driangle Over a year ago

no, the function priviliegedMethod has no way of accessing the privateVar. Like I said, that variable is constrained to the ChildClass() function

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