JavaScript: setTimeout Memory Leak Prevention.

setTimeout-mem-leak.js

// https://developer.mozilla.org/en-US/docs/Web/API/window.setTimeout

var timeoutID;
delayedAlert();

function delayedAlert() {
  timeoutID = window.setTimeout(slowAlert, 2000);
}

function slowAlert() {
  alert("That was really slow!");
  clearAlert();
}

function clearAlert() {
  window.clearTimeout(timeoutID);
}

1. If your code has the ability to call setTimeout frequently, it is useful to clear previous timers.

function delayedAlert() {
  if (timeoutID) {
    window.clearTimeout(timeoutID);
  }
  timeoutID = window.setTimeout(slowAlert, 2000);
}

2. Calling clearTimeout inside the slowAlert function is redundant because the timer has already completed its work, and clearTimeout cannot cancel the function execution after it has been called.