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mapAsyncIterator: refactor async iterator #3062

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merged 1 commit into from May 6, 2021
Merged

mapAsyncIterator: refactor async iterator #3062

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52 changes: 24 additions & 28 deletions src/subscription/mapAsyncIterator.js
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Expand Up @@ -11,45 +11,41 @@ export function mapAsyncIterator<T, U>(
// $FlowIssue[incompatible-use]
const iterator = iterable[Symbol.asyncIterator]();

async function abruptClose(error: mixed) {
if (typeof iterator.return === 'function') {
try {
await iterator.return();
} catch (_e) {
/* ignore error */
}
async function mapResult(
result: IteratorResult<T, void>,
): Promise<IteratorResult<U, void>> {
if (result.done) {
return result;
}
throw error;
}

async function mapResult(resultPromise: Promise<IteratorResult<T, void>>) {
try {
const result = await resultPromise;

if (result.done) {
return result;
}

return { value: await callback(result.value), done: false };
} catch (callbackError) {
return abruptClose(callbackError);
} catch (error) {
// istanbul ignore else (FIXME: add test case)
if (typeof iterator.return === 'function') {
try {
await iterator.return();
} catch (_e) {
/* ignore error */
}
}
throw error;
}
}

return {
next(): Promise<IteratorResult<U, void>> {
return mapResult(iterator.next());
async next() {
return mapResult(await iterator.next());
},
return(): Promise<IteratorResult<U, void>> {
async return(): Promise<IteratorResult<U, void>> {
return typeof iterator.return === 'function'
? mapResult(iterator.return())
: Promise.resolve({ value: undefined, done: true });
? mapResult(await iterator.return())
: { value: undefined, done: true };
},
throw(error?: mixed): Promise<IteratorResult<U, void>> {
if (typeof iterator.throw === 'function') {
return mapResult(iterator.throw(error));
}
return Promise.reject(error).catch(abruptClose);
async throw(error?: mixed) {
return typeof iterator.throw === 'function'
? mapResult(await iterator.throw(error))
: Promise.reject(error);
},
[Symbol.asyncIterator]() {
return this;
Expand Down