real-cancellable-promise
A simple cancellable promise implementation for JavaScript and TypeScript.
Read the announcement post for a full explanation. In particular, see the "Prior art" section for a comparison to existing cancellable promise libraries.
⚡ Compatible with fetch, axios, and jQuery.ajax🐦 Lightweight — zero dependencies and less than 1 kB minified and gzipped🏭 Used in production by Interface Technologies💻 Optimized for TypeScript⚛ Built with React in mind🔎 Compatible with react-query query cancellation out of the box
The Basics
yarn add real-cancellable-promise
import { CancellablePromise } from 'real-cancellable-promise';
const cancellablePromise = new CancellablePromise(normalPromise, cancel);
cancellablePromise.cancel();
await cancellablePromise; // throws a Cancellation object that subclasses Error
Important
The CancellablePromise
constructor takes in a promise
and a cancel
function.
Your cancel
function MUST cause promise
to reject with a Cancellation
object.
This will NOT work, your callbacks with still run:
new CancellablePromise(normalPromise, () => {});
Usage with HTTP Libraries
How do I convert a normal Promise
to a CancellablePromise
?
fetch
export function cancellableFetch(
input: RequestInfo,
init: RequestInit = {}
): CancellablePromise<Response> {
const controller = new AbortController();
const promise = fetch(input, {
...init,
signal: controller.signal,
}).catch((e) => {
if (e.name === 'AbortError') {
throw new Cancellation();
}
// rethrow the original error
throw e;
});
return new CancellablePromise<Response>(promise, () => controller.abort());
}
// Use just like normal fetch:
const cancellablePromise = cancellableFetch(url, {
/* pass options here */
});
fetch
with response handling
export function cancellableFetch<T>(
input: RequestInfo,
init: RequestInit = {}
): CancellablePromise<T> {
const controller = new AbortController();
const promise = fetch(input, {
...init,
signal: controller.signal,
})
.then((response) => {
// Handle the response object however you want
if (!response.ok) {
throw new Error(`Fetch failed with status code ${response.status}.`);
}
if (response.headers.get('content-type')?.includes('application/json')) {
return response.json();
} else {
return response.text();
}
})
.catch((e) => {
if (e.name === 'AbortError') {
throw new Cancellation();
}
// rethrow the original error
throw e;
});
return new CancellablePromise<T>(promise, () => controller.abort());
}
axios
export function cancellableAxios<T>(
config: AxiosRequestConfig
): CancellablePromise<T> {
const source = axios.CancelToken.source();
config = { ...config, cancelToken: source.token };
const promise = axios(config)
.then((response) => response.data)
.catch((e) => {
if (e instanceof axios.Cancel) {
throw new Cancellation();
}
// rethrow the original error
throw e;
});
return new CancellablePromise<T>(promise, () => source.cancel());
}
// Use just like normal axios:
const cancellablePromise = cancellableAxios({ url });
jQuery.ajax
export function cancellableJQueryAjax<T>(
settings: JQuery.AjaxSettings
): CancellablePromise<T> {
const xhr = $.ajax(settings);
const promise = xhr.catch((e) => {
if (e.statusText === 'abort') throw new Cancellation();
// rethrow the original error
throw e;
});
return new CancellablePromise<T>(promise, () => xhr.abort());
}
// Use just like normal $.ajax:
const cancellablePromise = cancellableJQueryAjax({ url, dataType: 'json' });
API Reference
CancellablePromise
supports all the methods that the normal Promise
object
supports, except Promise.any
(ES2021). See the API
Reference for details.
Examples
React: Cancel the API call when the component unmounts
If your React component makes an API call, you probably don't care about the result of that API call after the component has unmounted. You can cancel the API in the cleanup function of an effect like this:
function listBlogPosts(): CancellablePromise<Post[]> {
// call the API
}
export function Blog() {
const [posts, setPosts] = useState<Post[]>([]);
useEffect(() => {
const cancellablePromise = listBlogPosts()
.then(setPosts)
.catch(console.error);
// The promise will get canceled when the component unmounts
return cancellablePromise.cancel;
}, []);
return (
<div>
{posts.map((p) => {
/* ... */
})}
</div>
);
}
Before React 18, this was necessary to prevent the infamous "setState after unmount" warning. This warning was removed from React in React 18 because setting state after the component unmounts is usually not indicative of a real problem.
CodeSandbox: prevent setState after unmount
React: Cancel the in-progress API call when query parameters change
Sometimes API calls have parameters, like a search string entered by the user. If the query parameters change, you should cancel any in-progress API calls.
function searchUsers(searchTerm: string): CancellablePromise<User[]> {
// call the API
}
export function UserList() {
const [searchTerm, setSearchTerm] = useState('');
const [users, setUsers] = useState<User[]>([]);
// In a real app you should debounce the searchTerm
useEffect(() => {
const cancellablePromise = searchUsers(searchTerm)
.then(setUsers)
.catch(console.error);
// The old API call gets canceled whenever searchTerm changes. This prevents
// setUsers from being called with incorrect results if the API calls complete
// out of order.
return cancellablePromise.cancel;
}, [searchTerm]);
return (
<div>
<SearchInput searchTerm={searchTerm} onChange={setSearchTerm} />
{users.map((u) => {
/* ... */
})}
</div>
);
}
CodeSandbox: cancel the in-progress API call when query parameters change
Combine multiple API calls into a single async flow
The utility function buildCancellablePromise
lets you capture
every
cancellable operation in a multi-step process. In this example, if bigQuery
is
canceled, each of the 3 API calls will be canceled (though some might have
already completed).
function bigQuery(userId: number): CancellablePromise<QueryResult> {
return buildCancellablePromise(async (capture) => {
const userPromise = api.user.get(userId);
const rolePromise = api.user.listRoles(userId);
const [user, roles] = await capture(
CancellablePromise.all([userPromise, rolePromise])
);
// User must be loaded before this query can run
const customer = await capture(api.customer.get(user.customerId));
return { user, roles, customer };
});
}
react-query
Usage with If your query key changes and there's an API call in progress, react-query
will cancel the CancellablePromise
automatically.
CodeSandbox: react-query integration
Cancellation
Handling Usually, you'll want to ignore Cancellation
objects that get thrown:
try {
await capture(cancellablePromise);
} catch (e) {
if (e instanceof Cancellation) {
// do nothing — the component probably just unmounted.
// or you could do something here it's up to you 😆
return;
}
// log the error or display it to the user
}
Handling promises that can't truly be canceled
Sometimes you need to call an asynchronous function that doesn't support
cancellation. In this case, you can use pseudoCancellable
:
const cancellablePromise = pseudoCancellable(normalPromise);
// Later...
cancellablePromise.cancel();
await cancellablePromise; // throws Cancellation object if promise did not already resolve
CancellablePromise.delay
await CancellablePromise.delay(1000); // wait 1 second
Supported Platforms
Browser: anything that's not Internet Explorer.
React Native / Expo: should work in any recent release. AbortController
has been available since 0.60.
Node.js: 14+. AbortController
is only available in Node 15+. Both require()
(CommonJS) and import
(ES modules) are supported without use of a transpiler or bundler.
License
MIT
Contributing
See CONTRIBUTING.md
.