Async Generator

Motivated by the Async Generator ES7 proposal https://github.com/jhusain/asyncgenerator

A couple helper functions to bring async support to ES6 generators today:

• asyncIterator: Converts Promise<T[]> to Promise<T>[].
• asyncPager: Creates a generator function will iterate through a paging function.
• wrapObservable: Creates a generator function by wrapping an observable.

npm install async-generator

Examples

You'll need to include a polyfill for the regeneratorRuntime such as babel-polyfill

asyncIterator: Converts Promise<T[]> to Promise<T>[].

1import {asyncIterator} from 'async-generator';
2
3const items: Promise<T[]> = ...;
4
5for (let promise of asyncIterator(items)) {
6  const value: number = await promise;
7
8  // value will be undefined if the array returned is empty or undefined.
9  if (value !== undefined) {
10    doSomething(value);
11  }
12}

asyncPager: Repeatedly calls a paging function.

1import {asyncPager} from 'async-generator';
2
3// data consumer
4async function getPage(pageNumber: number) {
5  // ...e.g. web request
6  return null; // return null/undefined when there are no more pages.
7}
8
9for (let promise of asyncPager(getPage)) {
10  const value: number = await promise;
11
12  // value will be undefined if any page is empty.
13  if (value !== undefined) {
14    doSomething(value);
15  }
16}

wrapObservable: Wraps an Observable with an iterator

1import {wrapObservable} from 'async-generator';
2
3// data consumer
4const observable = ...;
5
6for (let promise of wrapObservable(observable)) {
7  const value: number = await promise;
8
9  // value will be undefined if any page is empty.
10  if (value !== undefined) {
11    doSomething(value);
12  }
13}