JavaScriptで簡単に数字をアニメーションでイージング変化

現在値:
移行値:
var b = document.getElementById('b');
b.addEventListener('click', function() {
  var rFrom = parseInt(document.getElementById('r').value, 10);
  var rTo = parseInt(document.getElementById('rr').value, 10);
  if(rFrom !== rTo) {
    var CALC_TIMES = 30;
    var SPEED = 50;
    var rReduce = Math.floor((rFrom - rTo) / CALC_TIMES);
    var timer = setInterval(function() {
        if(rFrom > (rTo + rReduce)) {
            rFrom -= rReduce;
            r.value = rFrom;
        }
        else {
          r.value = rTo;
          clearInterval(timer);
        }
    }, SPEED);
  }
}, false);