test262/test/language/statements/for-of/iterator-close-via-throw.js

// Copyright (C) 2015 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
description: >
    Iterators should be closed via their `return` method when iteration is
    interrupted via a `throw` statement.
features: [Symbol.iterator]
---*/

var startedCount = 0;
var returnCount = 0;
var iterationCount = 0;
var iterable = {};

iterable[Symbol.iterator] = function() {
  return {
    next: function() {
      startedCount += 1;
      return { done: false, value: null };
    },
    return: function() {
      returnCount += 1;
      return {};
    }
  };
};

try {
  for (var x of iterable) {
    assert.sameValue(
      startedCount, 1, 'Value is retrieved'
    );
    assert.sameValue(
      returnCount, 0, 'Iterator is not closed'
    );
    iterationCount += 1;
    throw 0;
  }
} catch (err) {}

assert.sameValue(
  startedCount, 1, 'Iterator does not restart following interruption'
);
assert.sameValue(iterationCount, 1, 'A single iteration occurs');
assert.sameValue(
  returnCount, 1, 'Iterator is closed after `throw` statement'
);