Edit in JSFiddle

(function(root){

    function F(){};

    root.inherits = function inherits(child, parent) {
        F.prototype = parent.prototype;
        //child.superClass_ = parent.prototype;
        child.prototype = new F();
        //child.prototype.constructor = child;
    }

})(this);



function Mammal(){
    console.log("I'm a mammal");
    this.whatwhat = "what";
}


function Cat(){
    console.log("CAT WHAT: " + this.whatwhat );
    Mammal.call(this);
    console.log("I'm a cat");   
    console.log("CAT WHAT: " + this.whatwhat );
}

var c1 = new Cat();

inherits(Cat, Mammal);

var c2 = new Cat();

console.log(c1.constructor, c2.constructor);
console.log(typeof(c1), typeof(c2));
console.log(Object.prototype.toString.call(c1), Object.prototype.toString.call(c2));