Count animation from number A to B

Question

I am updating a numeric value inside an element by doing intervalled ajax requests.

To make the whole thing a bit more alive,

Answer 1

I used a mixture of all of these to create a function that updates a BehaviorSubject.

function animateValue(subject, timerRef, startValue, endValue, duration){
  if (timerRef) {  clearInterval(timerRef); }
  const minInterval = 100;
  const valueRange = endValue - startValue;
  const startTime = new Date().getTime();
  const endTime = startTime + (duration * 1000);
  const interval = Math.max((endTime-startTime)/valueRange, minInterval);

  function run() {
    const now = new Date().getTime();
    const rangePercent = Math.min(1-((endTime-now)/(endTime-startTime)),1);
    const value = Math.round(rangePercent * valueRange+startValue);

    subject.next(value);
    if (rangePercent >= 1) {
      clearInterval(timerRef);
    }
  }

  timerRef = setInterval(run, interval);
  run();
}