Async iterator helpers

Modules

esnext.async-iterator.constructor, esnext.async-iterator.drop, esnext.async-iterator.every, esnext.async-iterator.filter, esnext.async-iterator.find, esnext.async-iterator.flat-map, esnext.async-iterator.for-each, esnext.async-iterator.from, esnext.async-iterator.map, esnext.async-iterator.reduce, esnext.async-iterator.some, esnext.async-iterator.take, esnext.async-iterator.to-array, esnext.iterator.to-async.

Built-ins signatures

class Iterator {
  toAsync(): AsyncIterator<any>;
}

class AsyncIterator {
  static from(iterable: AsyncIterable<any> | Iterable<any> | AsyncIterator<any>): AsyncIterator<any>;
  drop(limit: uint): AsyncIterator<any>;
  every(async callbackfn: (value: any, counter: uint) => boolean): Promise<boolean>;
  filter(async callbackfn: (value: any, counter: uint) => boolean): AsyncIterator<any>;
  find(async callbackfn: (value: any, counter: uint) => boolean): Promise<any>;
  flatMap(async callbackfn: (value: any, counter: uint) => AsyncIterable<any> | Iterable<any> | AsyncIterator<any>): AsyncIterator<any>;
  forEach(async callbackfn: (value: any, counter: uint) => void): Promise<void>;
  map(async callbackfn: (value: any, counter: uint) => any): AsyncIterator<any>;
  reduce(async callbackfn: (memo: any, value: any, counter: uint) => any, initialValue?: any): Promise<any>;
  some(async callbackfn: (value: any, counter: uint) => boolean): Promise<boolean>;
  take(limit: uint): AsyncIterator<any>;
  toArray(): Promise<Array>;
  @@toStringTag: 'AsyncIterator';
}

Entry points

core-js/proposals/async-iterator-helpers
core-js(-pure)/actual|full/async-iterator
core-js(-pure)/actual|full/async-iterator/drop
core-js(-pure)/actual|full/async-iterator/every
core-js(-pure)/actual|full/async-iterator/filter
core-js(-pure)/actual|full/async-iterator/find
core-js(-pure)/actual|full/async-iterator/flat-map
core-js(-pure)/actual|full/async-iterator/for-each
core-js(-pure)/actual|full/async-iterator/from
core-js(-pure)/actual|full/async-iterator/map
core-js(-pure)/actual|full/async-iterator/reduce
core-js(-pure)/actual|full/async-iterator/some
core-js(-pure)/actual|full/async-iterator/take
core-js(-pure)/actual|full/async-iterator/to-array
core-js(-pure)/actual|full/iterator/to-async

Examples

await AsyncIterator.from([1, 2, 3, 4, 5, 6, 7])
  .drop(1)
  .take(5)
  .filter(it => it % 2)
  .map(it => it ** 2)
  .toArray();  // => [9, 25]

await [1, 2, 3].values().toAsync().map(async it => it ** 2).toArray(); // => [1, 4, 9]

Caveats

To prevent prototype pollution, in the pure version, new %AsyncIteratorPrototype% methods are not added to the real %AsyncIteratorPrototype%, they are available only on wrappers - instead of [].values().toAsync().map(fn) use AsyncIterator.from([]).map(fn).
Now, we have access to the real %AsyncIteratorPrototype% only by using the async generators syntax. So, for compatibility of the library with old browsers, we should use the Function constructor. However, that breaks compatibility with CSP. So, if you want to use the real %AsyncIteratorPrototype%, you should set USE_FUNCTION_CONSTRUCTOR option in the core-js/configurator to true:

const configurator = require('core-js/configurator');

configurator({ USE_FUNCTION_CONSTRUCTOR: true });

require('core-js/actual/async-iterator');

(async function * () { /* empty */ })() instanceof AsyncIterator; // => true

As an alternative, you could pass to the core-js/configurator an object that will be considered as %AsyncIteratorPrototype%:

const configurator = require('core-js/configurator');

const { getPrototypeOf } = Object;

configurator({ AsyncIteratorPrototype: getPrototypeOf(getPrototypeOf(getPrototypeOf(async function * () { /* empty */ }()))) });

require('core-js/actual/async-iterator');

(async function * () { /* empty */ })() instanceof AsyncIterator; // => true