--- /dev/null
+'use strict';
+// https://github.com/tc39/proposal-iterator-helpers
+var $ = require('../internals/export');
+var aFunction = require('../internals/a-function');
+var anObject = require('../internals/an-object');
+var createAsyncIteratorProxy = require('../internals/async-iterator-create-proxy');
+var getAsyncIteratorMethod = require('../internals/get-async-iterator-method');
+
+var AsyncIteratorProxy = createAsyncIteratorProxy(function (arg, Promise) {
+ var state = this;
+ var mapper = state.mapper;
+ var innerIterator, iteratorMethod;
+
+ return new Promise(function (resolve, reject) {
+ var outerLoop = function () {
+ try {
+ Promise.resolve(anObject(state.next.call(state.iterator, arg))).then(function (step) {
+ try {
+ if (anObject(step).done) {
+ state.done = true;
+ resolve({ done: true, value: undefined });
+ } else {
+ Promise.resolve(mapper(step.value)).then(function (mapped) {
+ try {
+ iteratorMethod = getAsyncIteratorMethod(mapped);
+ if (iteratorMethod !== undefined) {
+ state.innerIterator = innerIterator = anObject(iteratorMethod.call(mapped));
+ state.innerNext = aFunction(innerIterator.next);
+ return innerLoop();
+ } reject(TypeError('.flatMap callback should return an iterable object'));
+ } catch (error2) { reject(error2); }
+ }, reject);
+ }
+ } catch (error1) { reject(error1); }
+ }, reject);
+ } catch (error) { reject(error); }
+ };
+
+ var innerLoop = function () {
+ if (innerIterator = state.innerIterator) {
+ try {
+ Promise.resolve(anObject(state.innerNext.call(innerIterator))).then(function (result) {
+ try {
+ if (anObject(result).done) {
+ state.innerIterator = state.innerNext = null;
+ outerLoop();
+ } else resolve({ done: false, value: result.value });
+ } catch (error1) { reject(error1); }
+ }, reject);
+ } catch (error) { reject(error); }
+ } else outerLoop();
+ };
+
+ innerLoop();
+ });
+});
+
+$({ target: 'AsyncIterator', proto: true, real: true }, {
+ flatMap: function flatMap(mapper) {
+ return new AsyncIteratorProxy({
+ iterator: anObject(this),
+ mapper: aFunction(mapper),
+ innerIterator: null,
+ innerNext: null
+ });
+ }
+});