Can't change scrollbar values

I've made a simple code to change the value of a scrollbar along with document.scrollTop but i can't get it to work.Can someone tell me where i've made a mistake(s) ?

        var scroll = document.scrollTop; 
        var container = document.getElementById('test');
        container.innerHTML = scroll;

     var pb = document.getElementById('progress-bar');
        pb.value = 2;
        var change = function()
        {   pb.value = 2;
              pb.value++;
        };

        if (scroll > 0){
            change();
        };