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DigitalBrainJS edited this page Oct 17, 2021 · 6 revisions

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CPromise2

This lib provides CPromise class - an advanced version of the built-in Promise that supports:

  • deep cancellation through rejection. All static methods like all/race/allSettled support cancellation.
  • all & allSettled method support concurrency limitation and generators as promise producers
  • advanced progress capturing
  • flat async code writing using generators/yield as an alternative of async/await
  • event data flows (upstream & downstream)
  • pause & resume ability
  • timeouts
  • retries
  • AbortController support (providing & subscribing for multiple signals sources)
  • atomic subchains - such chains will be completed if the execution has been started, even if its upper chain received a Cancel signal.

Installation 🔨

npm:

$ npm install c-promise2

yarn:

$ yarn add c-promise2

CDN:

Quick start

  • Import CPromise class:
import { CPromise } from "c-promise2";
  • Use CPromise constructor instead of Promise. To terminate internal async tasks (timers, request, streams etc.) gracefully subscribe your cleanup handler with onCancel(handler):
const doTask = (ms)=>{
  return CPromise((resolve, reject, {onCancel})=>{
    const timer= setTimeout(resolve, ms, "myValue");
    onCancel(()=> clearTimeout(timer));
  });
}

const promise = doTask(1000).then(console.log);

Or/and turn generators to async functions with CPromise.promisify to write cancellable async code in flat style:

const doTask = CPromise.promisify(function*(ms){
  yield CPromise.delay(ms);
  return "myValue";
});

const promise = doTask(1000).then(console.log);
  • Call promise.cancel([reason]) to cancel pending promise chain by rejecting the deepest pending promise in the chain with a special CanceledError reason:
promise.cancel("My bad");

Basic example

Building plain CPromise chains using then

Codesandbox Live Demo

import { CPromise } from "c-promise2";

const promise= new CPromise((resolve, reject, {onCancel, onPause, onResume})=>{
    onCancel(()=>{
        //optionally some code here to abort your long-term task (abort request, stop timers etc.)
    });
}).then(
    value => console.log(`Done: ${value}`), 
    (err, scope) => {
        console.warn(`Failed: ${err}`); // Failed: CanceledError: canceled
        console.log('chain isCanceled:', promise.isCanceled); // true
        console.log('promise isCanceled:', scope.isCanceled); // true
    }
);

console.log('isPromise:', promise instanceof Promise); // true

setTimeout(()=> promise.cancel(), 1000);

Log:

isPromise: true
Failed: CanceledError: canceled 
chain isCanceled: true
promise isCanceled: true

Writing flat code using generators

Codesandbox Live Demo

import { CPromise } from "c-promise2";

const sayHello = CPromise.promisify(function* (v) {
  for (let i = 0; i < 3; i++) {
    console.log(`Hello [${i}]`);
    yield CPromise.delay(1000);
  }
  return v + 1;
});

const p = sayHello(5)
  .then(function* (v) {
    console.log(`Then`);
    yield CPromise.delay(1000);
    return v + 1;
  })
  .then((v) => console.log(`Done: ${v}`));

// setTimeout(() => p.cancel(), 1000); stop trying

Abortable fetch with timeout

This is how an abortable fetch (live example) with a timeout might look like

function fetchWithTimeout(url, {timeout, ...fetchOptions}= {}) {
   return new CPromise((resolve, reject, {signal}) => {
      fetch(url, {...fetchOptions, signal}).then(resolve, reject)
   }, {timeout, nativeController: true})
}

const promise= fetchWithTimeout('http://localhost/', {timeout: 5000})
      .then(response => response.json())
      .then(data => console.log(`Done: `, data), err => console.log(`Error: `, err))

setTimeout(()=> promise.cancel(), 1000); 

// you able to call cancel() at any time to cancel the entire chain at any stage
// the related network request will also be aborted

Note

You can use the cp-fetch which provides a ready to use CPromise wrapper for cross-platform fetch API, or cp-axios wrapper for axios with powers of CPromise.

.then method behavior notes

The behavior of the method is slightly different from native Promise. In the case when you cancel the chain after it has been resolved within one eventloop tick, onRejected will be called with a CanceledError instance, instead of onFulfilled. This prevents the execution of unwanted code in the next eventloop tick if the user canceled the promise immediately after the promise was resolved, during the same eventloop tick.

Ecosystem

React

Data fetching

Backend

  • cp-koa - a wrapper for koa, that implements cancellable middlewares/routes to the framework

License

The MIT License Copyright (c) 2020 Dmitriy Mozgovoy [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.

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