Wait for the Fastest JavaScript Promise to Settle with Promise.race()

I am curious. Do you know about any actual use cases for Promise.race? I had no need to use that ever.

I am curious. Do you know about any actual use cases for Promise.race? I had no need to use that ever.

A common use case for racing promises is to create a time out on the client. You can send a request and race that request with a timeout of whatever length you give it, passing Promise.reject to the timeout handler.

@Daniel: I've almost never used Promise.race() either, but this course wouldn't have been complete without it.

As Ian and I mentioned, racing a promise against a timeout promise is a possible use case. Another scenario might be fetching the same information from two different sources and only waiting for the faster response.

I get an error message: TypeError: Promise.race(...).finally is not a function

function resolveAfter(ms, value) {
  return new Promise((resolve) => {
    setTimeout(() => {
      resolve(value);
    }, ms);
  });
}

function timeout(ms, measuringPromise) {
  let timeoutID;
  const timeoutPromise = new Promise((_, reject) => {
    timeoutID = setTimeout(() => {
      reject(Error(`Timed out after ${ms}ms`));
    }, ms);
  });

  return Promise.race([somePromise, timeoutPromise]).finally(() => {
    clearTimeout(timeoutID);
  });
}

const somePromise = resolveAfter(1000, 'Some Content');

timeout(2000, somePromise).then(
  (value) => console.log(value),
  (err) => console.warn(error.message),
);

Node v8.17.0, MacOS Catalina v10.15.6

@Erkan: The Promise.prototype.finally method is only supported as of Node v10.0.0 (see https://node.green/#ES2018-features-Promise-prototype-finally).

thank you very much, that must have been the scotch at that time, alread got it,..