2 // https://github.com/tc39/proposal-iterator-helpers
3 var $ = require('../internals/export');
4 var aFunction = require('../internals/a-function');
5 var anObject = require('../internals/an-object');
6 var getIteratorMethod = require('../internals/get-iterator-method');
7 var createIteratorProxy = require('../internals/iterator-create-proxy');
8 var iteratorClose = require('../internals/iterator-close');
10 var IteratorProxy = createIteratorProxy(function (arg) {
11 var iterator = this.iterator;
12 var mapper = this.mapper;
13 var result, mapped, iteratorMethod, innerIterator;
17 if (innerIterator = this.innerIterator) {
18 result = anObject(this.innerNext.call(innerIterator));
19 if (!result.done) return result.value;
20 this.innerIterator = this.innerNext = null;
23 result = anObject(this.next.call(iterator, arg));
25 if (this.done = !!result.done) return;
27 mapped = mapper(result.value);
28 iteratorMethod = getIteratorMethod(mapped);
30 if (iteratorMethod === undefined) {
31 throw TypeError('.flatMap callback should return an iterable object');
34 this.innerIterator = innerIterator = anObject(iteratorMethod.call(mapped));
35 this.innerNext = aFunction(innerIterator.next);
37 iteratorClose(iterator);
43 $({ target: 'Iterator', proto: true, real: true }, {
44 flatMap: function flatMap(mapper) {
45 return new IteratorProxy({
46 iterator: anObject(this),
47 mapper: aFunction(mapper),