Stack implementation using ES6 proxies

stack.js

/*
 * Another ES6 Proxy experiment. This one creates a stack whose underlying
 * implementation is an array. The proxy is used to filter out everything
 * but "push", "pop", and "length" from the interface, making it a pure
 * stack where you can't manipulate the contents.
 */

var Stack = (function(){

    var stack = [],
        allowed = [ "push", "pop", "length" ];
    
    return Proxy.create({
        get: function(receiver, name){;
            if (allowed.indexOf(name) > -1){
                if(typeof stack[name] == "function"){
                    return stack[name].bind(stack);
                } else {
                    return stack[name];
                }
            } else {
                return undefined;
            }
        }
    
    });

});

var mystack = new Stack();

mystack.push("hi");
mystack.push("goodbye");

console.log(mystack.length);    //1

console.log(mystack[0]);        //undefined
console.log(mystack.pop());     //"goodbye"