What is the best general practice to timeout a function in promise [closed]

Answer 1

The native Promise.race method doesn't clear the timer of the timeout promise after the actual promise completes thus the process will wait until the timeout promise is also complete. This means that if you set the timeout to 1h and our promise is completed after 1min then the process will wait for 59min before it exits.

Use this method instead:

export function race({promise, timeout, error}) {
  let timer = null;

  return Promise.race([
    new Promise((resolve, reject) => {
      timer = setTimeout(reject, timeout, error);
      return timer;
    }),
    promise.then((value) => {
      clearTimeout(timer);
      return value;
    })
  ]);
}

Answer 2

It depends on what you mean by timeout.

If you expect the function to stop, then no.

If you just want to stop waiting for it, then yes (quick to whip up in ES6):

var wait = ms => new Promise(resolve => setTimeout(resolve, ms));
var timeout = (p, ms) => Promise.race([p, wait(ms).then(() => {
    throw new Error("Timeout after " + ms + " ms");
})]);

var wait = ms => new Promise(resolve => setTimeout(resolve, ms));
var timeout = (p, ms) => Promise.race([p, wait(ms).then(() => {
  throw new Error("Timeout after " + ms + " ms");
})]);

// Example:

var log = msg => div.innerHTML += "<p>" + msg + "</p>";
var failed = e => log(e.toString() + ", line " + e.lineNumber);

log("Waiting 5 seconds...");
timeout(wait(5000), 2000)
.then(() => log("...Done."))
.catch(failed);

<div id="div"></div>

If you want to cancel the operation (make it stop), then hopefully that operation comes with an API to cancel it, and you should use that, since an ES6 promise is not a control surface.

Cancelable promises is a controversial topic in ES6, but some of the libraries mentioned do offer the concept.