| /** |
| * Given an AsyncIterable and a callback function, return an AsyncIterator |
| * which produces values mapped via calling the callback function. |
| */ |
| export function mapAsyncIterator(iterable, callback) { |
| const iterator = iterable[Symbol.asyncIterator](); |
| |
| async function mapResult(result) { |
| if (result.done) { |
| return result; |
| } |
| |
| try { |
| return { |
| value: await callback(result.value), |
| done: false, |
| }; |
| } catch (error) { |
| /* c8 ignore start */ |
| // FIXME: add test case |
| if (typeof iterator.return === 'function') { |
| try { |
| await iterator.return(); |
| } catch (_e) { |
| /* ignore error */ |
| } |
| } |
| |
| throw error; |
| /* c8 ignore stop */ |
| } |
| } |
| |
| return { |
| async next() { |
| return mapResult(await iterator.next()); |
| }, |
| |
| async return() { |
| // If iterator.return() does not exist, then type R must be undefined. |
| return typeof iterator.return === 'function' |
| ? mapResult(await iterator.return()) |
| : { |
| value: undefined, |
| done: true, |
| }; |
| }, |
| |
| async throw(error) { |
| if (typeof iterator.throw === 'function') { |
| return mapResult(await iterator.throw(error)); |
| } |
| |
| throw error; |
| }, |
| |
| [Symbol.asyncIterator]() { |
| return this; |
| }, |
| }; |
| } |