4.0 KiB
Executable File
p-cancelable 
Create a promise that can be canceled
Useful for animation, loading resources, long-running async computations, async iteration, etc.
Install
$ npm install p-cancelable
Usage
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);
API
new PCancelable(executor)
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 PCancelable = require('p-cancelable');
const cancelablePromise = new PCancelable((resolve, reject, onCancel) => {
const job = new Job();
onCancel.shouldReject = false;
onCancel(() => {
job.stop();
});
job.on('finish', resolve);
});
cancelablePromise.cancel(); // Doesn't throw an error
PCancelable is a subclass of Promise.
onCanceled(fn)
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.
PCancelable#cancel([reason])
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.
PCancelable#isCanceled
Type: boolean
Whether the promise is canceled.
PCancelable.CancelError
Type: Error
Rejection reason when .cancel() is called.
It includes a .isCanceled property for convenience.
PCancelable.fn(fn)
Convenience method to make your promise-returning or async function cancelable.
The function you specify will have onCancel appended to its parameters.
const PCancelable = require('p-cancelable');
const fn = PCancelable.fn((input, onCancel) => {
const job = new Job();
onCancel(() => {
job.cleanup();
});
return job.start(); //=> Promise
});
const cancelablePromise = fn('input'); //=> PCancelable
// …
cancelablePromise.cancel();
FAQ
Cancelable vs. Cancellable
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.
What about the official Cancelable Promises proposal?
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.
Related
- p-progress - Create a promise that reports progress
- p-lazy - Create a lazy promise that defers execution until
.then()or.catch()is called - More…
License
MIT © Sindre Sorhus