Throttled Event Handling in JavaScript

throttled-event-handler.js

/**
 * Attach an event listener to an object. Invokes the handle()
 * callback on every event, and the apply() handler eventually, but
 * with at least 'delay' milliseconds between each invokation.
 */
function addThrottledEventHandler(elem, event, handle, apply, delay) {
  let nextApply = performance.now();
  let timerId = null;
  function invokeApply() { apply(); timerId = null; }
  elem.addEventListener(event, (ev) => {
    if (handle !== null)
      handle(ev);
    let now = performance.now();
    if (now < nextApply) {
      if (timerId === null) {
        timerId = setTimeout(invokeApply, nextApply - now);
        nextApply += delay;
      }
    } else {
      apply();
      nextApply = now + delay;
    }
  });
}