test262/test/language/statements/for-of/iterator-next-reference.js

// Copyright (C) 2013 the V8 project authors. All rights reserved.
// This code is governed by the BSD license found in the LICENSE file.
/*---
es6id: 13.6.4.13 S5.c
description: >
    The iterator's `next` method should be accessed with each iteration as per
    the `IteratorStep` abstract operation (7.4.5).
features: [Symbol.iterator]
---*/

var iterable = {};
var iterator = {};
var firstIterResult = { done: false };
var iterationCount, invocationCount;

iterable[Symbol.iterator] = function() {
  return iterator;
};

iterator.next = function() { return { value: 45, done: false }; };
iterationCount = 0;
invocationCount = 0;
for (var x of iterable) {
  assert.sameValue(x, 45);

  iterator.next = function() {
    invocationCount++;

    Object.defineProperty(iterator, 'next', {
      get: function() {
        $ERROR('Should not access the `next` method after iteration ' +
          'is complete.');
      }
    });

    return { value: null, done: true };
  };
  iterationCount++;
}
assert.sameValue(iterationCount, 1);
assert.sameValue(invocationCount, 1);