75 lines
2.3 KiB
Plaintext
75 lines
2.3 KiB
Plaintext
// @flow strict
|
|
import { SYMBOL_ASYNC_ITERATOR } from '../polyfills/symbols';
|
|
|
|
import type { PromiseOrValue } from '../jsutils/PromiseOrValue';
|
|
|
|
/**
|
|
* Given an AsyncIterable and a callback function, return an AsyncIterator
|
|
* which produces values mapped via calling the callback function.
|
|
*/
|
|
export default function mapAsyncIterator<T, U>(
|
|
iterable: AsyncIterable<T> | AsyncGenerator<T, void, void>,
|
|
callback: (T) => PromiseOrValue<U>,
|
|
rejectCallback?: (any) => PromiseOrValue<U>,
|
|
): AsyncGenerator<U, void, void> {
|
|
// $FlowFixMe[prop-missing]
|
|
const iteratorMethod = iterable[SYMBOL_ASYNC_ITERATOR];
|
|
const iterator: any = iteratorMethod.call(iterable);
|
|
let $return: any;
|
|
let abruptClose;
|
|
if (typeof iterator.return === 'function') {
|
|
$return = iterator.return;
|
|
abruptClose = (error: mixed) => {
|
|
const rethrow = () => Promise.reject(error);
|
|
return $return.call(iterator).then(rethrow, rethrow);
|
|
};
|
|
}
|
|
|
|
function mapResult(result: IteratorResult<T, void>) {
|
|
return result.done
|
|
? result
|
|
: asyncMapValue(result.value, callback).then(iteratorResult, abruptClose);
|
|
}
|
|
|
|
let mapReject;
|
|
if (rejectCallback) {
|
|
// Capture rejectCallback to ensure it cannot be null.
|
|
const reject = rejectCallback;
|
|
mapReject = (error: mixed) =>
|
|
asyncMapValue(error, reject).then(iteratorResult, abruptClose);
|
|
}
|
|
|
|
/* TODO: Flow doesn't support symbols as keys:
|
|
https://github.com/facebook/flow/issues/3258 */
|
|
return ({
|
|
next(): Promise<IteratorResult<U, void>> {
|
|
return iterator.next().then(mapResult, mapReject);
|
|
},
|
|
return() {
|
|
return $return
|
|
? $return.call(iterator).then(mapResult, mapReject)
|
|
: Promise.resolve({ value: undefined, done: true });
|
|
},
|
|
throw(error?: mixed): Promise<IteratorResult<U, void>> {
|
|
if (typeof iterator.throw === 'function') {
|
|
return iterator.throw(error).then(mapResult, mapReject);
|
|
}
|
|
return Promise.reject(error).catch(abruptClose);
|
|
},
|
|
[SYMBOL_ASYNC_ITERATOR]() {
|
|
return this;
|
|
},
|
|
}: $FlowFixMe);
|
|
}
|
|
|
|
function asyncMapValue<T, U>(
|
|
value: T,
|
|
callback: (T) => PromiseOrValue<U>,
|
|
): Promise<U> {
|
|
return new Promise((resolve) => resolve(callback(value)));
|
|
}
|
|
|
|
function iteratorResult<T>(value: T): IteratorResult<T, void> {
|
|
return { value, done: false };
|
|
}
|