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await-timeout

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    await-timeout

A Promise-based API for setTimeout / clearTimeout


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await-timeout

A Promise-based API for setTimeout / clearTimeout
Build Status Npm version License

Contents

Installation

npm install await-timeout --save

Usage

  1. Just wait some time:

    import Timeout from 'await-timeout';
    
    // wait 1000 ms and resolve
    await Timeout.set(1000);
    
    // wait 1000 ms and reject with 'Error'
    await Timeout.set(1000, 'Error');
    
  2. Use Timeout instance inside try...finally block to make proper cleanup:

    import Timeout from 'await-timeout';
    
    const timer = new Timeout();
    try {
      await Promise.race([
        fetch('https://example.com'),
        timer.set(1000)
          .then(() => Promise.reject('Timeout'))
      ]);
    } finally {
      timer.clear();
    }
    

API

new Timeout()

Constructs new timeout instance. It does not start timer but creates variable for timer manipulation.

const timer = new Timeout();

Note: having separate variable is useful for clearing timeout in finally block

.set(ms, [message]) ⇒ Promise

Starts new timer like setTimeout() and returns promise. The promise will be resolved after ms milliseconds:

const timer = new Timeout();
timer.set(1000)
  .then(() => console.log('1000 ms passed.'));

If you need to reject after timeout:

timer.set(1000)
  .then(() => {throw new Error('Timeout')});

Or reject with custom error:

timer.set(1000)
  .then(() => {throw new MyTimeoutError()});

The second parameter message is just convenient way to reject with new Error(message):

timer.set(1000, 'Timeout');
// is equivalent to
timer.set(1000).then(() => {throw new Error('Timeout')});

If you need to just wait some time - use static version of .set():

await Timeout.set(1000);

.wrap(promise, ms, [message]) ⇒ Promise

Wraps existing promise with timeout:

  • promise automatically rejected after timeout
  • timeout automatically cleared if promise fulfills first
const promise = fetch('https://example.com');

const timeoutedPromise = Timeout.wrap(promise, 1000, 'Timeout');

Actually it is a shortcut for:

const promise = fetch('https://example.com');

const timer = new Timeout();
try {
  const timeoutedPromise = await Promise.race([
    promise,
    timer.set(1000, 'Timeout')
  ]);
} finally {
  timer.clear();
}

.clear()

Clears existing timeout like clearTimeout().

const timer = new Timeout();
timer.set(1000)
  .then(() => console.log('This will never be called, because timeout is cleared on the next line'));
timer.clear();

With ES7 async / await .clear() can be used in finally block:

async function foo() {
  const timer = new Timeout();
  try {
    // some async stuff
  } finally {
    timer.clear();
  }
}

Motivation

Before making this library I've researched many similar packages on Npm. But no one satisfied all my needs together:

  1. Convenient way to cancel timeout. I typically use it with Promise.race() and don't want timer to trigger if main promise is fulfilled first.
  2. API similar to setTimeout / clearTimeout. I get used to these functions and would like to have mirror syntax.
  3. Easy rejection of timeout promise. Passing error message should be enough.
  4. No monkey-patching of Promise object.
  5. Zero dependencies.

License

MIT @ Vitaliy Potapov

Keywords

FAQs

Last updated on 10 May 2019

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