DigitalBrainJS
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/allSettledsupport cancellation. all&allSettledmethod support concurrency limitation and generators as promise producers- advanced progress capturing
- flat async code writing using
generators/yieldas an alternative ofasync/await - event data flows (upstream & downstream)
pause&resumeability- timeouts
- retries
AbortControllersupport (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 :hammer:
npm:
$ npm install c-promise2yarn:
$ yarn add c-promise2CDN:
production UMD version (or minified ~11KB) - provides the CPromise class as the default export, other exports values declared as static properties
Quick start
- Import CPromise class:
import { CPromise } from "c-promise2";- Use
CPromiseconstructor instead ofPromise. To terminate internal async tasks (timers, request, streams etc.) gracefully subscribe your cleanup handler withonCancel(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 specialCanceledErrorreason:promise.cancel("My bad");
Basic example
Building plain CPromise chains using then
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: ${err}`); // Failed: CanceledError: canceled
console.log('chain isCanceled:', promise.isCanceled); // true
console.log('promise isCanceled:', scope.isCanceled); // true
}
);
console.log('isPromise:', promise instanceof Promise); // true
setTimeout(()=> promise.cancel(), 1000);Log:
isPromise: true
Failed: CanceledError: canceled
chain isCanceled: true
promise isCanceled: trueWriting flat code using generators
import { CPromise } from "c-promise2";
const sayHello = CPromise.promisify(function* (v) {
for (let i = 0; i < 3; i++) {
console.log(`Hello [${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 tryingAbortable 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 abortedNote
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
- use-async-effect2 - feature-rich React async hooks that built on top of the cancellable promises (CPromise)
Data fetching
- cp-axios - axios cancellable wrapper that supports CPromise context. Can be directly used in use-async-effect2 or general CPromise context
- cp-fetch - cross-platform fetch wrapper that can be used in cooperation with use-async-effect2 or general CPromise chains
Backend
Learn more
See CPromise wiki
API Reference
JSDoc autogenerated API Reference
License
The MIT License Copyright (c) 2020 Dmitriy Mozgovoy robotshara@gmail.com
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.