Sleep

https://www.greatfrontend.com/questions/javascript/sleep?practice=practice&tab=coding

In JavaScript, the setTimeout function can be used to execute callbacks after a delay. However, it introduces a layer of nesting in the code which may not be desired. It'd be nice to use setTimeout in this fashion:

// Note: the following code contains invalid syntax and doesn't work.
console.log('Hello!');
setTimeout(1000);
console.log('Bye.');

In languages like Java and Python, a sleep function is available to suspend execution of the calling thread. However, unlike other languages, JavaScript is single-threaded and blocking the main thread is not a good idea. Hence lets implement an asynchronous version of the sleep function that works similarly but does not block the main thread.

Examples

async function greeting() {
  console.log('Hello!');
  await sleep(2000);
  console.log('Bye.'); // Only logs after 2000 milliseconds (2 seconds)
}

greeting();
// t = 0: Hello!
// t = 2000: Bye.

The sleep function should also be able to be used without await:

console.log('Hello!');
sleep(2000).then(() => {
  console.log('Bye.'); // Only logs after 2000 milliseconds (2 seconds)
});

Editorial

Solution

Approach 1: Non-blocking using setTimeout

1. The sleep function takes a duration parameter representing the time in milliseconds for which the execution should be paused.
2. It returns a Promise that will resolve after the specified duration.
3. Inside the Promise constructor, use setTimeout to delay the execution of the resolve function, effectively pausing the execution for the specified time.

/**
 * @param {number} duration
 * @return {Promise<void>}
 */
export default async function sleep(duration) {
  return new Promise((resolve) => setTimeout(resolve, duration));
}

Approach 2: Blocking version of sleep()

A synchronous, blocking version of sleep repeatedly checks if duration has passed since the function started running. It pauses all execution on the main thread.

function sleep(duration) {
  let now = new Date().getTime();
  while (new Date().getTime() < now + duration) {
    // Do nothing.
  }
  // Proceed when `duration` has passed since `now`.
}

Asynchronous sleep example