JavaScript Quick Tip: Create A Cancelable Promise Delay

JavaScript Quick Tip: Create A Cancelable Promise Delay

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You might see the need to wait for a short period before you do a certain action from time to time. JavaScript has setTimeout for this, and it works perfectly fine. But what if you want to work with Promises and perhaps even async/await?

setTimeout breaks this pattern because it takes a callback. But gladly, we can combine both to create a delayed Promise you can await if you want.

The Code

const delay = (delay, value) => {
  let timeout;
  let _reject;
  const promise = new Promise((resolve, reject) => {
    _reject = reject;
    timeout = setTimeout(resolve, delay, value);
  });
  return {
    promise,
    cancel() {
      if (timeout) {
        clearTimeout(timeout);
        timeout = null;
        _reject();
        _reject = null;
      }
    }
  };
};

Usage

You can then use it like this afterward:

const delayed = delay(5000, "This value is returned by the promise");

// This await only returns after at least 5 seconds.
// Execution is halted before it continues after the
// Promise resolves.
const value = await delayed.promise;

// more operations...

And if you want to take advantage of being able to cancel it, you can use it like this:

const delayed = delay(5000, "value");
delayed.promise
  .then((value) => console.log(value))
  .catch(() => console.error("Rejected"));

// This will be executed before the promise fires. 
// Thus, the Promise is canceled and
// the catch is executed.
delayed.cancel();

The Whole Tip As An Image

If you like visual content more, or if you want to store it for later, I put all this into one single image for you. I hope you like it!

A picture showcasing the above code

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