javascript object prototype property access

Question

Here is a jsFiddle of my question: http://jsfiddle.net/4wyvv/1/

Basically:

//constructor function
function Maker(){
    var str;

    this.init = function(str){
        this.str = str;
    };

    this.msg = function(){
        return this.str;
    };
}

//object from Maker
var obj = new Maker();

obj.init("Hi my name is Dan");

//make sure everything exists and has worked as expected
Audit.Log(obj.msg());
//look in Maker.prototype for the constructor property
Audit.Log(obj.constructor);
//look in Maker.prototype for the constructor property
Audit.Log(Maker.prototype.constructor);

//now look for all makers prototype properties, this should list atleast "constructor"
for(var i in Maker.prototype){
    Audit.Log(i);
}

Why does the foreach loop not put out anything? It should at least put out constructor as I showed that Maker.prototype.constructor exists.

Answer 1

From MDN

for..in Iterates over the enumerable properties of an object, in arbitrary order. For each distinct property, statements can be executed.

Things like constructor , toString , hasOwnProperty are non enumerable properties and they won't be listed in for..in

Answer 2

Some properties of object like "constructor" are hidden or to be more precise non-enumerable so they are not enumerated using a for in loop like this, In ECMA5 we have a method that can get all the properties

Object.getOwnPropertyNames(Maker.prototype)

this is give you

["constructor"]

Here is a detailed explanation : How to display all methods of an object in Javascript?