CancellablePromise

An extension of the Promise class that allows for cancellation.

Installation

npm i @wondermonger/cancellable-promise

Usage

Prerequisites

• node@>=10.0.0

API

new CancellablePromise(executor, [signal])

• executor {Function} executor function (required)
  • resolve {Function} function that fulfills a CancellablePromise with a given value (required)
  • [reject] {Function} function that rejects a CancellablePromise with a given reason
  • [onCancel] {Function} function for handling cancellation within the excecutor function -- the AbortError must still be handled outside of the excecutor function
• [signal] {AbortSignal} AbortController signal property
• returns {CancellablePromise} a CancellablePromise instance

CancellablePromise.prototype.cancel([message])

• [message] {String} AbortError instance message

CancellablePromise.prototype.catchCancel(onCancellation)

• onCancellation {Function} cancellation error handling function -- if cancellations are not handled by CancellablePromise.prototype.catchCancel they must be handled by CancellablePromise.prototype.catch or they will result in an uncaught AbortError (required)

CancellablePromise extends Promise

• see Promise documentation for more information

Code Examples

'use strict';

const CancellablePromise = require("@wondermonger/cancellable-promise");

const promise = new CancellablePromise((resolve, reject, onCancel) => {
  const timeout = setTimeout(() => {
    console.info("timeout complete");
    resolve("Foo");
  }, 5000);
  onCancel(() => {
    clearTimeout(timeout);
    console.info("timeout cleared");
  });
});

setTimeout(() => promise.cancel(), 2500);

promise
  .then(value => console.info("never called"))
  .catchCancel((abortError) => console.warn("cancellation caught here"))
  .catch(error => console.error("never called"));

promise
  .then(value => console.info("never called"))
  .catch(error => console.error("cancellation caught here when .catchCancel() not called earlier in chain"));

promise
  .then(value => console.info("never called"))
  .catch(error => console.error("cancellation caught here when .catchCancel() not called earlier in chain"))
  .catchCancel((abortError) => console.warn("never called because cancellation was already caught by .catch()"));

promise
  .then(value => console.info("never called and AbortError is unhandled"));

Using AbortController

'use strict';

const AbortController = require("abort-controller");
const CancellablePromise = require("@wondermonger/cancellable-promise");

const controller = new AbortController();
const promise = new CancellablePromise((resolve, reject, onCancel) => {
  const timeout = setTimeout(() => {
    console.info("timeout complete");
    resolve("Foo");
  }, 5000);
  onCancel(() => {
    clearTimeout(timeout);
    console.info("timeout cleared");
  });
}, controller.signal);

setTimeout(() => controller.abort(), 2500);

promise
  .then(value => console.info("never called"))
  .catchCancel((abortError) => console.warn("cancellation caught here"))
  .catch(error => console.error("never called"));

Async Functions

'use strict';

const CancellablePromise = require("@wondermonger/cancellable-promise");

const promise = new CancellablePromise((resolve, reject, onCancel) => {
  const timeout = setTimeout(() => {
    console.info("timeout complete");
    resolve("Foo");
  }, 5000);
  onCancel(() => {
    clearTimeout(timeout);
    console.info("timeout cleared");
  });
});

setTimeout(() => promise.cancel(), 2500);

const someAsyncFunction = async () => {
  try {
    const value = await promise;
    console.info("never called");
    return value;
  } catch (err) {
    if (err && err.name === "AbortError") {
      console.warn("cancellation caught here"));
      return "Bar";
    }
    console.error("never called");
  }
};

const anotherAsyncFunction = async () => {
  try {
    const value = await promise.catchCancel((abortError) => {
      console.warn("cancellation caught here");
      return "Bar";
    });
    console.info("resolved value is `Bar`");
    return value;
  } catch (err) {
    console.error("never called");
  }
};

Using AbortController with Promise

It requires some additional effort, but you can use an AbortController with an unextended Promise. You may not need this library.

Development

Merge requests should be submitted to https://gitlab.com/wondermonger/cancellable-promise.

Installation

npm i

Linting

npm run lint

Testing

# all tests
npm run test

# unit tests
npm run test:unit

# coverage tests
npm run test:coverage

License

The MIT License (MIT)

Copyright (c) 2020 Michael J. Bondra [email protected]

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.