33 lines
1.1 KiB
JavaScript
33 lines
1.1 KiB
JavaScript
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export default async function* combine(iterable) {
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const asyncIterators = Array.from(iterable, o => o[Symbol.asyncIterator]());
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const results = [];
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let count = asyncIterators.length;
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const never = new Promise(() => {});
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function getNext(asyncIterator, index) {
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return asyncIterator.next().then(result => ({
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index,
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result,
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}));
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}
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const nextPromises = asyncIterators.map(getNext);
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try {
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while (count) {
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const {index, result} = await Promise.race(nextPromises);
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if (result.done) {
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nextPromises[index] = never;
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results[index] = result.value;
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count--;
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} else {
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nextPromises[index] = getNext(asyncIterators[index], index);
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yield result.value;
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}
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}
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} finally {
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for (const [index, iterator] of asyncIterators.entries())
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if (nextPromises[index] != never && iterator.return != null)
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iterator.return();
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// no await here - see https://github.com/tc39/proposal-async-iteration/issues/126
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}
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return results;
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}
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