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p-cancelable
Advanced tools
Package description
The p-cancelable package provides a way to create cancelable promises in JavaScript. This is particularly useful for managing asynchronous operations that may need to be canceled before they complete, such as HTTP requests, long-running computations, or any other task that might not need to continue executing if certain conditions are met.
Creating a cancelable promise
This feature allows the creation of a new cancelable promise. The promise can be canceled at any time before it resolves or rejects, which triggers the onCancel function where cleanup operations like clearing timeouts or aborting requests can be performed.
const PCancelable = require('p-cancelable');
const myCancelablePromise = new PCancelable((resolve, reject, onCancel) => {
const timer = setTimeout(() => {
resolve('Done!');
}, 2000);
onCancel(() => {
clearTimeout(timer);
reject(new Error('Operation canceled.'));
});
});
myCancelablePromise.cancel();
Bluebird is a comprehensive promise library that includes support for cancelable promises. Compared to p-cancelable, Bluebird offers a broader set of promise-related utilities, such as map, reduce, and filter for promises, making it suitable for more complex scenarios.
The abort-controller package provides a way to abort one or more Web API tasks, such as Fetch API requests, by using an AbortSignal. While it serves a similar purpose for canceling tasks, it is specifically designed to work with the Fetch API and other APIs that support aborting, unlike p-cancelable which is more generic.
Readme
Create a promise that can be canceled
Useful for animation, loading resources, long-running async computations, async iteration, etc.
$ npm install p-cancelable
const PCancelable = require('p-cancelable');
const cancelablePromise = new PCancelable((resolve, reject, onCancel) => {
const worker = new SomeLongRunningOperation();
onCancel(() => {
worker.close();
});
worker.on('finish', resolve);
worker.on('error', reject);
});
(async () => {
try {
console.log('Operation finished successfully:', await cancelablePromise);
} catch (error) {
if (cancelablePromise.isCanceled) {
// Handle the cancelation here
console.log('Operation was canceled');
return;
}
throw error;
}
})();
// Cancel the operation after 10 seconds
setTimeout(() => {
cancelablePromise.cancel('Unicorn has changed its color');
}, 10000);
Same as the Promise
constructor, but with an appended onCancel
parameter in executor
.
Cancelling will reject the promise with PCancelable.CancelError
. To avoid that, set onCancel.shouldReject
to false
.
const cancelable = new PCancelable((resolve, reject, onCancel) => {
const job = new Job();
onCancel.shouldReject = false;
onCancel(() => {
job.stop();
});
job.on('finish', resolve);
});
promise.cancel(); // Doesn't throw an error
PCancelable
is a subclass of Promise
.
Type: Function
Accepts a function that is called when the promise is canceled.
You're not required to call this function. You can call this function multiple times to add multiple cancel handlers.
Type: Function
Cancel the promise and optionally provide a reason.
The cancellation is synchronous. Calling it after the promise has settled or multiple times does nothing.
Type: boolean
Whether the promise is canceled.
Type: Error
Rejection reason when .cancel()
is called.
It includes a .isCanceled
property for convenience.
Convenience method to make your promise-returning or async function cancelable.
The function you specify will have onCancel
appended to its parameters.
const fn = PCancelable.fn((input, onCancel) => {
const job = new Job();
onCancel(() => {
job.cleanup();
});
return job.start(); //=> Promise
});
const promise = fn('input'); //=> PCancelable
// …
promise.cancel();
In American English, the verb cancel is usually inflected canceled and canceling—with one l.
Both a browser API and the Cancelable Promises proposal use this spelling.
It's still an early draft and I don't really like its current direction. It complicates everything and will require deep changes in the ecosystem to adapt to it. And the way you have to use cancel tokens is verbose and convoluted. I much prefer the more pragmatic and less invasive approach in this module. The proposal was withdrawn.
.then()
or .catch()
is calledMIT © Sindre Sorhus
FAQs
Create a promise that can be canceled
The npm package p-cancelable receives a total of 16,918,930 weekly downloads. As such, p-cancelable popularity was classified as popular.
We found that p-cancelable demonstrated a not healthy version release cadence and project activity because the last version was released a year ago. It has 1 open source maintainer collaborating on the project.
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