Implement a resumable interval function

Apr 03, 2024

resumeInterval is a utility function using which we can create intervals that can be paused, restarted and stopped.

It takes the same signature as window.setInterval() and returns an object with the following methods:

start: executes the callback immediately and every interval seconds.
paused: pauses the running interval. Calling start again should restart the interval again.
stop: permanently stops the interval. Once stopped, intervals can be started or paused again.

1. Basic implementation

function createResumableInterval(callback, delay, ...args) {
  let timerId = null;
  let hasStopped = false;

  function pause() {
    // if stopped we return
    if (hasStopped) {
      return;
    }

    // we can stop only when timer id running, i.e timerId exists
    if (timerId) {
      clearInterval(timerId);
      timerId = null;
    }
  }

  function start() {
    // if hasStopped, we return
    if (hasStopped) {
      return;
    }

    // we can start only when there is no timerId present
    if (!timerId) {
      callback();
      timerId = setInterval(callback, delay, ...args);
    }
  }

  function stop() {
    // we can stop only created timers
    if (!hasStopped && timerId) {
      hasStopped = true;
      clearInterval(timerId);
    }
  }

  return {
    start,
    stop,
    pause
  };
}

let count = 0;

const interval = createResumableInterval(() => {
  count++;
  console.log(count);
}, 1000);

interval.start();

setTimeout(() => {
  interval.pause();
}, 3500);

setTimeout(() => {
  interval.start();
}, 4500);

setTimeout(() => {
  interval.stop();
}, 6000);