module.js

//a constructor
function Thing(a, b, c, d){
    //a private constructor
    function Thing(){ 
        //we don't care about d
        this.d = d;
    }
    
    //a is read-only
    Thing.prototype.getA = function(){ return a; };
    
    //b is read/write
    Thing.prototype.getB = function(){ return b; };
    Thing.prototype.setB = function(newB){ b = newB; };
    
    //augment c
    c = c.toString();
    
    //c augments the value
    Thing.prototype.getC = function(){ return c; };
    Thing.prototype.setC = function(newC){ c = newC.toString(); };
    
    return new Thing();
}

//usage
var myThing = new Thing(1,2,3,4);

myThing.a; // does not exist
myThing.b; // does not exist
myThing.c; // does not exist
myThing.d; // a public property

myThing.getA(); //return 1

myThing.getB(); //return 2
myThing.setB(8);
myThing.getB(); //return 8

myThing.getC(); //return "3"
myThing.setC(9);
myThing.getC(); //return "9"

//caveats
myThing instanceof Thing; //false, but expectation is true
myThing.constructor.name; //"Thing" -- this is because we used the same name