function animate(elemname, duration_ms, step_ms) {
        var elem = document.getElementById(elemname);
        var start_time = new Date();
        var x = 0;
        do {
          elem.style.left = x;
          x = (x + 10) % 200;
          hold(step_ms);
        } while (duration_ms > new Date() - start_time);
      }

      function par(a, b) {
        alert("all done");
      }

      par(animate("animated_element_1", 10000, 100),
          animate("animated_element_2", 7000, 80));