The for-await-of
syntax is similar to the for-of
iteration. The key difference is that it automatically awaits any promises generated by the iterator. This lesson covers how to consume async data sources easily with for-await-of
.
for-await-of
essentially allows you to use async/await
in a generator function.
import { magic } from './server'; (Symbol as any).asyncIterator = (Symbol as any).asyncIterator || Symbol.for("Symbol.asyncIterator"); async function* numbers() { let index = 1; while (true) { yield index; index = await magic(index); if (index > 10) { break; } } } async function main() { for await (const num of numbers()) { console.log(num); } } main();
Server:
const magic = (i: number) => new Promise<number>(res => setTimeout(res(i + 1), 100));
Example 2:
// Asynchronous generators async function asyncGenerators () { async function* createAsyncIterable(syncIterable) { for (const elem of syncIterable) { yield elem; } } const asyncGenObj = createAsyncIterable(['a', 'b']); const [{value:v1}, {value:v2}] = await Promise.all([ asyncGenObj.next(), asyncGenObj.next() ]); console.log("v1", v1, "v2", v2); // a, b } asyncGenerators();