var firstf = function () {
    var counter = 0;
    return function () {
           console.log("counter = " + counter);
           return counter += 1;
           }
    };
var add = firstf();
add();//output 0
add();//output 1
add();//output 2
firstf()();//output 0
firstf()();//output 0
firstf()();//output 0