[async-iteration] add support for for-await-of loops in Async Functions

test/mjsunit/harmony/for-await-of.js

+// Copyright 2017 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Flags: --harmony-async-iteration --allow-natives-syntax
+
+let testFailed = false;
+let testFailure;
+(async function() {
+  const kNext = 1;
+  const kThrow = 2;
+  const kReturn = 4;
+
+  function async(iterable, features = kNext, log = []) {
+    // Helper to turn a synchronous iterable into an asynchronous iterable,
+    // without using the [Async-from-Sync Iterator].
+    let it = iterable[Symbol.iterator]();
+    let methods = {
+      next(sentValue) {
+        return new Promise(function(resolve, reject) {
+          let {value, done} = it.next(sentValue);
+          Promise.resolve(value).then(function(value) {
+            log.push('.next() -> resolved ' + value);
+            resolve({value, done});
+          }, function(value) {
+            log.push('.next() -> rejected ' + value);
+            reject(value);
+          });
+        });
+      },
+
+      throw(sentValue) {
+        return new Promise(function(resolve, reject) {
+          let throwMethod = it.throw;
+          if (typeof throwMethod !== 'function') {
+            log.push('.throw(' + sentValue + ')');
+            return reject(sentValue);
+          }
+
+          let {value, done} = throwMethod.call(it, sentValue);
+          Promise.resolve(value).then(function(value) {
+                log.push('.throw() -> resolved ' + value);
+                resolve({ value, done });
+              }, function(value) {
+                log.push('.throw() -> rejected ' + value);
+                reject(value);
+              });
+        });
+      },
+
+      return(sentValue) {
+        return new Promise(function(resolve, reject) {
+          let returnMethod = it.return;
+          if (typeof returnMethod !== 'function') {
+            log.push('.return(' + sentValue + ')');
+            return resolve({value: sentValue, done: true});
+          }
+
+          let {value, done} = returnMethod.call(it, sentValue);
+          Promise.resolve(value).then(function(value) {
+            log.push('.return() -> resolved ' + value);
+            resolve({ value, done });
+          }, function(value) {
+            log.push('.return() -> rejected ' + value);
+            reject(value);
+          });
+        });
+      }
+    };
+
+
+    return {
+      [Symbol.asyncIterator]() {
+        log.push('[Symbol.asyncIterator]()')
+        return this;
+      },
+
+      next: (features & kNext) ? methods.next : undefined,
+      throw: (features & kThrow) ? methods.throw : undefined,
+      return: (features & kReturn) ? methods.return : undefined
+    };
+  }
+
+  let testDone;
+  let test;
+  async function testBindingIdentifierVarDeclarationStatement() {
+    let sum = 0;
+    testDone = false;
+    for await (var value of async([100, 200, 300, 400, 500])) sum += value;
+    testDone = true;
+    return sum;
+  }
+
+  test = testBindingIdentifierVarDeclarationStatement();
+  assertFalse(testDone);
+  assertEquals(1500, await test);
+  assertTrue(testDone);
+
+  async function testBindingIdentifierVarDeclarationBlockStatement() {
+    let sum = 0;
+    testDone = false;
+    for await (var value of async([100, 200, 300, 400, 500])) {
+      'use strict';
+      let strict = (function() { return this === undefined; })();
+      assertFalse(strict);
+      sum += value;
+    }
+    testDone = true;
+    return sum;
+  }
+
+  test = testBindingIdentifierVarDeclarationBlockStatement();
+  assertFalse(testDone);
+  assertEquals(1500, await test);
+  assertTrue(testDone);
+
+  async function testObjectBindingPatternVarDeclarationStatement() {
+    let sum = 0, keys = [];
+    let collection = [
+      {key: 'first', value: 10}, {key: undefined, value: 20}, {value: 30},
+      {key: 'last', value: 40}
+    ];
+    testDone = false;
+    for await (var {key = 'unknown', value} of async(collection))
+        keys.push(key), sum += value;
+    testDone = true;
+    return {keys, sum};
+  }
+
+  test = testObjectBindingPatternVarDeclarationStatement();
+  assertFalse(testDone);
+  assertEquals(
+      {keys: ['first', 'unknown', 'unknown', 'last'], sum: 100}, await test);
+  assertTrue(testDone);
+
+  async function testObjectBindingPatternVarDeclarationBlockStatement() {
+    let sum = 0, keys = [];
+    let collection = [
+      {key: 'first', value: 10}, {key: undefined, value: 20}, {value: 30},
+      {key: 'last', value: 40}
+    ];
+    testDone = false;
+    for await (var {key = 'unknown', value} of async(collection)) {
+      'use strict';
+      let strict = (function() { return this === undefined; })();
+      assertFalse(strict);
+      keys.push(key);
+      sum += value;
+    }
+    testDone = true;
+    return {keys, sum};
+  }
+
+  test = testObjectBindingPatternVarDeclarationBlockStatement();
+  assertFalse(testDone);
+  assertEquals(
+      {keys: ['first', 'unknown', 'unknown', 'last'], sum: 100}, await test);
+  assertTrue(testDone);
+
+  async function testArrayBindingPatternVarDeclarationStatement() {
+    let sum = 0, keys = [];
+    let collection = [['first', 10], [undefined, 20], [, 30], ['last', 40]];
+    testDone = false;
+    for await (var [key = 'unknown', value] of async(collection))
+        keys.push(key), sum += value;
+    testDone = true;
+    return {keys, sum};
+  }
+
+  test = testArrayBindingPatternVarDeclarationStatement();
+  assertFalse(testDone);
+  assertEquals(
+      {keys: ['first', 'unknown', 'unknown', 'last'], sum: 100}, await test);
+  assertTrue(testDone);
+
+  async function testArrayBindingPatternVarDeclarationBlockStatement() {
+    let sum = 0, keys = [];
+    let collection = [['first', 10], [undefined, 20], [, 30], ['last', 40]];
+    testDone = false;
+    for await (var [key = 'unknown', value] of async(collection)) {
+      'use strict';
+      let strict = (function() { return this === undefined; })();
+      assertFalse(strict);
+      keys.push(key);
+      sum += value;
+    }
+    testDone = true;
+    return {keys, sum};
+  }
+
+  test = testArrayBindingPatternVarDeclarationBlockStatement();
+  assertFalse(testDone);
+  assertEquals(
+      {keys: ['first', 'unknown', 'unknown', 'last'], sum: 100}, await test);
+  assertTrue(testDone);
+
+  // --------------------------------------------------------------------------
+
+  async function testBindingIdentifierLetDeclarationStatement() {
+    let sum = 0;
+    testDone = false;
+    for await (let value of async([100, 200, 300, 400, 500])) sum += value;
+    testDone = true;
+    return sum;
+  }
+
+  test = testBindingIdentifierLetDeclarationStatement();
+  assertFalse(testDone);
+  assertEquals(1500, await test);
+  assertTrue(testDone);
+
+  async function testBindingIdentifierLetDeclarationBlockStatement() {
+    let sum = 0;
+    testDone = false;
+    for await (let value of async([100, 200, 300, 400, 500])) {
+      'use strict';
+      let strict = (function() { return this === undefined; })();
+      assertFalse(strict);
+      sum += value;
+    }
+    testDone = true;
+    return sum;
+  }
+
+  test = testBindingIdentifierLetDeclarationBlockStatement();
+  assertFalse(testDone);
+  assertEquals(1500, await test);
+  assertTrue(testDone);
+
+  async function testObjectBindingPatternLetDeclarationStatement() {
+    let sum = 0, keys = [];
+    let collection = [
+      {key: 'first', value: 10}, {key: undefined, value: 20}, {value: 30},
+      {key: 'last', value: 40}
+    ];
+    testDone = false;
+    for await (let {key = 'unknown', value} of async(collection))
+        keys.push(key), sum += value;
+    testDone = true;
+    return {keys, sum};
+  }
+
+  test = testObjectBindingPatternLetDeclarationStatement();
+  assertFalse(testDone);
+  assertEquals(
+      {keys: ['first', 'unknown', 'unknown', 'last'], sum: 100}, await test);
+  assertTrue(testDone);
+
+  async function testObjectBindingPatternLetDeclarationBlockStatement() {
+    let sum = 0, keys = [];
+    let collection = [
+      {key: 'first', value: 10}, {key: undefined, value: 20}, {value: 30},
+      {key: 'last', value: 40}
+    ];
+    testDone = false;
+    for await (let {key = 'unknown', value} of async(collection)) {
+      'use strict';
+      let strict = (function() { return this === undefined; })();
+      assertFalse(strict);
+      keys.push(key);
+      sum += value;
+    }
+    testDone = true;
+    return {keys, sum};
+  }
+
+  test = testObjectBindingPatternLetDeclarationBlockStatement();
+  assertFalse(testDone);
+  assertEquals(
+      {keys: ['first', 'unknown', 'unknown', 'last'], sum: 100}, await test);
+  assertTrue(testDone);
+
+  async function testObjectBindingPatternTDZLetDeclarationStatement() {
+    // See https://codereview.chromium.org/1218543003
+    let sum = 0;
+    testDone = false;
+    let value = { value: 1 };
+    try {
+      for await (let {value} of async([value])) sum += value;
+    } catch (error) {
+      testDone = true;
+      throw { sum, error, toString() { return 'TestError' } };
+    }
+    assertUnreachable('Awaited promise should be rejected');
+  }
+
+  test = testObjectBindingPatternTDZLetDeclarationStatement();
+  assertTrue(testDone); // Promise rejected before first Await
+  try {
+    await test;
+    assertUnreachable('Awaited promise should be rejected');
+  } catch (e) {
+    assertEquals('TestError', e.toString());
+    assertEquals(0, e.sum);
+    assertInstanceof(e.error, ReferenceError);
+  }
+
+  async function testObjectBindingPatternTDZLetDeclarationBlockStatement() {
+    // See https://codereview.chromium.org/1218543003
+    let sum = 0;
+    testDone = false;
+    let value = { value: 1 };
+    try {
+      for await (let {value} of async([value])) {
+        sum += value;
+      }
+    } catch (error) {
+      testDone = true;
+      throw { sum, error, toString() { return 'TestError' } };
+    }
+    assertUnreachable('Awaited promise should be rejected');
+  }
+
+  test = testObjectBindingPatternTDZLetDeclarationBlockStatement();
+  assertTrue(testDone); // Promise rejected before first Await
+  try {
+    await test;
+    assertUnreachable('Awaited promise should be rejected');
+  } catch (e) {
+    assertEquals('TestError', e.toString());
+    assertEquals(0, e.sum);
+    assertInstanceof(e.error, ReferenceError);
+  }
+
+  async function testArrayBindingPatternLetDeclarationStatement() {
+    let sum = 0, keys = [];
+    let collection = [['first', 10], [undefined, 20], [, 30], ['last', 40]];
+    testDone = false;
+    for await (let [key = 'unknown', value] of async(collection))
+        keys.push(key), sum += value;
+    testDone = true;
+    return {keys, sum};
+  }
+
+  test = testArrayBindingPatternLetDeclarationStatement();
+  assertFalse(testDone);
+  assertEquals(
+      {keys: ['first', 'unknown', 'unknown', 'last'], sum: 100}, await test);
+  assertTrue(testDone);
+
+  async function testArrayBindingPatternLetDeclarationBlockStatement() {
+    let sum = 0, keys = [];
+    let collection = [['first', 10], [undefined, 20], [, 30], ['last', 40]];
+    testDone = false;
+    for await (let [key = 'unknown', value] of async(collection)) {
+      'use strict';
+      let strict = (function() { return this === undefined; })();
+      assertFalse(strict);
+      keys.push(key);
+      sum += value;
+    }
+    testDone = true;
+    return {keys, sum};
+  }
+
+  test = testArrayBindingPatternLetDeclarationBlockStatement();
+  assertFalse(testDone);
+  assertEquals(
+      {keys: ['first', 'unknown', 'unknown', 'last'], sum: 100}, await test);
+  assertTrue(testDone);
+
+  async function testArrayBindingPatternTDZLetDeclarationStatement() {
+    // See https://codereview.chromium.org/1218543003
+    let sum = 0;
+    testDone = false;
+    let value = [1];
+    try {
+      for await (let [value] of async([value])) sum += value;
+    } catch (error) {
+      testDone = true;
+      throw { sum, error, toString() { return 'TestError' } };
+    }
+    assertUnreachable('Awaited promise should be rejected');
+  }
+
+  test = testArrayBindingPatternTDZLetDeclarationStatement();
+  assertTrue(testDone); // Promise rejected before first Await
+  try {
+    await test;
+    assertUnreachable('Awaited promise should be rejected');
+  } catch (e) {
+    assertEquals('TestError', e.toString());
+    assertEquals(0, e.sum);
+    assertInstanceof(e.error, ReferenceError);
+  }
+
+  async function testArrayBindingPatternTDZLetDeclarationBlockStatement() {
+    // See https://codereview.chromium.org/1218543003
+    let sum = 0;
+    testDone = false;
+    let value = [1];
+    try {
+      for await (let [value] of async([value])) {
+        sum += value;
+      }
+    } catch (error) {
+      testDone = true;
+      throw { sum, error, toString() { return 'TestError' } };
+    }
+    assertUnreachable('Awaited promise should be rejected');
+  }
+
+  test = testArrayBindingPatternTDZLetDeclarationBlockStatement();
+  assertTrue(testDone); // Promise rejected before first Await
+  try {
+    await test;
+    assertUnreachable('Awaited promise should be rejected');
+  } catch (e) {
+    assertEquals('TestError', e.toString());
+    assertEquals(0, e.sum);
+    assertInstanceof(e.error, ReferenceError);
+  }
+
+  // --------------------------------------------------------------------------
+
+  async function testBindingIdentifierConstDeclarationStatement() {
+    let sum = 0;
+    testDone = false;
+    for await (let value of async([100, 200, 300, 400, 500])) sum += value;
+    testDone = true;
+    return sum;
+  }
+
+  test = testBindingIdentifierConstDeclarationStatement();
+  assertFalse(testDone);
+  assertEquals(1500, await test);
+  assertTrue(testDone);
+
+  async function testBindingIdentifierConstDeclarationBlockStatement() {
+    let sum = 0;
+    testDone = false;
+    for await (const value of async([100, 200, 300, 400, 500])) {
+      'use strict';
+      // Ensure strict mode applies to block with use-strict-directive
+      let strict = (function() { return this === undefined; })();
+      assertFalse(strict);
+      sum += value;
+    }
+    testDone = true;
+    return sum;
+  }
+
+  test = testBindingIdentifierConstDeclarationBlockStatement();
+  assertFalse(testDone);
+  assertEquals(1500, await test);
+  assertTrue(testDone);
+
+  async function testObjectBindingPatternConstDeclarationStatement() {
+    let sum = 0, keys = [];
+    let collection = [
+      {key: 'first', value: 10}, {key: undefined, value: 20}, {value: 30},
+      {key: 'last', value: 40}
+    ];
+    testDone = false;
+    for await (const {key = 'unknown', value} of async(collection))
+        keys.push(key), sum += value;
+    testDone = true;
+    return {keys, sum};
+  }
+
+  test = testObjectBindingPatternConstDeclarationStatement();
+  assertFalse(testDone);
+  assertEquals(
+      {keys: ['first', 'unknown', 'unknown', 'last'], sum: 100}, await test);
+  assertTrue(testDone);
+
+  async function testObjectBindingPatternConstDeclarationBlockStatement() {
+    let sum = 0, keys = [];
+    let collection = [
+      {key: 'first', value: 10}, {key: undefined, value: 20}, {value: 30},
+      {key: 'last', value: 40}
+    ];
+    testDone = false;
+    for await (const {key = 'unknown', value} of async(collection)) {
+      'use strict';
+      let strict = (function() { return this === undefined; })();
+      assertFalse(strict);
+      keys.push(key);
+      sum += value;
+    }
+    testDone = true;
+    return {keys, sum};
+  }
+
+  test = testObjectBindingPatternConstDeclarationBlockStatement();
+  assertFalse(testDone);
+  assertEquals(
+      {keys: ['first', 'unknown', 'unknown', 'last'], sum: 100}, await test);
+  assertTrue(testDone);
+
+  async function testObjectBindingPatternTDZConstDeclarationStatement() {
+    // See https://codereview.chromium.org/1218543003
+    let sum = 0;
+    testDone = false;
+    const value = { value: 1 };
+    try {
+      for await (const {value} of async([value])) sum += value;
+    } catch (error) {
+      testDone = true;
+      throw { sum, error, toString() { return 'TestError' } };
+    }
+    assertUnreachable('Awaited promise should be rejected');
+  }
+
+  test = testObjectBindingPatternTDZConstDeclarationStatement();
+  assertTrue(testDone); // Promise rejected before first Await
+  try {
+    await test;
+    assertUnreachable('Awaited promise should be rejected');
+  } catch (e) {
+    assertEquals('TestError', e.toString());
+    assertEquals(0, e.sum);
+    assertInstanceof(e.error, ReferenceError);
+  }
+
+  async function testObjectBindingPatternTDZConstDeclarationBlockStatement() {
+    // See https://codereview.chromium.org/1218543003
+    let sum = 0;
+    testDone = false;
+    const value = { value: 1 };
+    try {
+      for await (const {value} of async([value])) {
+        sum += value;
+      }
+    } catch (error) {
+      testDone = true;
+      throw { sum, error, toString() { return 'TestError' } };
+    }
+    assertUnreachable('Awaited promise should be rejected');
+  }
+
+  test = testObjectBindingPatternTDZConstDeclarationBlockStatement();
+  assertTrue(testDone); // Promise rejected before first Await
+  try {
+    await test;
+    assertUnreachable('Awaited promise should be rejected');
+  } catch (e) {
+    assertEquals('TestError', e.toString());
+    assertEquals(0, e.sum);
+    assertInstanceof(e.error, ReferenceError);
+  }
+
+  async function testArrayBindingPatternConstDeclarationStatement() {
+    let sum = 0, keys = [];
+    let collection = [['first', 10], [undefined, 20], [, 30], ['last', 40]];
+    testDone = false;
+    for await (const [key = 'unknown', value] of async(collection))
+        keys.push(key), sum += value;
+    testDone = true;
+    return {keys, sum};
+  }
+
+  test = testArrayBindingPatternConstDeclarationStatement();
+  assertFalse(testDone);
+  assertEquals(
+      {keys: ['first', 'unknown', 'unknown', 'last'], sum: 100}, await test);
+  assertTrue(testDone);
+
+  async function testArrayBindingPatternConstDeclarationBlockStatement() {
+    let sum = 0, keys = [];
+    let collection = [['first', 10], [undefined, 20], [, 30], ['last', 40]];
+    testDone = false;
+    for await (const [key = 'unknown', value] of async(collection)) {
+      'use strict';
+      let strict = (function() { return this === undefined; })();
+      assertFalse(strict);
+      keys.push(key);
+      sum += value;
+    }
+    testDone = true;
+    return {keys, sum};
+  }
+
+  test = testArrayBindingPatternLetDeclarationBlockStatement();
+  assertFalse(testDone);
+  assertEquals(
+      {keys: ['first', 'unknown', 'unknown', 'last'], sum: 100}, await test);
+  assertTrue(testDone);
+
+  async function testArrayBindingPatternTDZConstDeclarationStatement() {
+    // See https://codereview.chromium.org/1218543003
+    let sum = 0;
+    testDone = false;
+    const value = [1];
+    try {
+      for await (const [value] of async([value])) sum += value;
+    } catch (error) {
+      testDone = true;
+      throw { sum, error, toString() { return 'TestError' } };
+    }
+    assertUnreachable('Awaited promise should be rejected');
+  }
+
+  test = testArrayBindingPatternTDZConstDeclarationStatement();
+  assertTrue(testDone); // Promise rejected before first Await
+  try {
+    await test;
+    assertUnreachable('Awaited promise should be rejected');
+  } catch (e) {
+    assertEquals('TestError', e.toString());
+    assertEquals(0, e.sum);
+    assertInstanceof(e.error, ReferenceError);
+  }
+
+  async function testArrayBindingPatternTDZConstDeclarationBlockStatement() {
+    // See https://codereview.chromium.org/1218543003
+    let sum = 0;
+    testDone = false;
+    const value = [1];
+    try {
+      for await (const [value] of async([value])) {
+        sum += value;
+      }
+    } catch (error) {
+      testDone = true;
+      throw { sum, error, toString() { return 'TestError' } };
+    }
+    assertUnreachable('Awaited promise should be rejected');
+  }
+
+  test = testArrayBindingPatternTDZConstDeclarationBlockStatement();
+  assertTrue(testDone); // Promise rejected before first Await
+  try {
+    await test;
+    assertUnreachable('Awaited promise should be rejected');
+  } catch (e) {
+    assertEquals('TestError', e.toString());
+    assertEquals(0, e.sum);
+    assertInstanceof(e.error, ReferenceError);
+  }
+
+  // --------------------------------------------------------------------------
+
+  async function testBindingIdentifierLHSStatement() {
+    let sum = 0;
+    let value;
+    testDone = false;
+    for await (value of async([100, 200, 300, 400, 500])) sum += value;
+    testDone = true;
+    return sum;
+  }
+
+  test = testBindingIdentifierLHSStatement();
+  assertFalse(testDone);
+  assertEquals(1500, await test);
+  assertTrue(testDone);
+
+  async function testBindingIdentifierLHSBlockStatement() {
+    let sum = 0;
+    let value;
+    testDone = false;
+    for await (value of async([100, 200, 300, 400, 500])) {
+      'use strict';
+      let strict = (function() { return this === undefined; })();
+      assertFalse(strict);
+      sum += value;
+    }
+    testDone = true;
+    return sum;
+  }
+
+  test = testBindingIdentifierLHSStatement();
+  assertFalse(testDone);
+  assertEquals(1500, await test);
+  assertTrue(testDone);
+
+  async function testObjectBindingPatternLHSStatement() {
+    let sum = 0;
+    let keys = [];
+    let value;
+    let key;
+    let collection = [
+      {key: 'first', value: 1}, {key: undefined, value: 2}, {value: 3},
+      {key: 'last', value: 4}
+    ];
+    testDone = false;
+    for await ({key = 'unknown', value} of async(collection))
+        keys.push(key), sum += value;
+    testDone = true;
+    return {keys, sum};
+  }
+
+  test = testObjectBindingPatternLHSStatement();
+  assertFalse(testDone);
+  assertEquals(
+      {keys: ['first', 'unknown', 'unknown', 'last'], sum: 10}, await test);
+  assertTrue(testDone);
+
+  async function testObjectBindingPatternLHSBlockStatement() {
+    let sum = 0;
+    let keys = [];
+    let value;
+    let key;
+    let collection = [
+      {key: 'first', value: 1}, {key: undefined, value: 2}, {value: 3},
+      {key: 'last', value: 4}
+    ];
+    testDone = false;
+    for await ({key = 'unknown', value} of async(collection)) {
+      'use strict';
+      let strict = (function() { return this === undefined; })();
+      assertFalse(strict);
+      keys.push(key);
+      sum += value;
+    }
+    testDone = true;
+    return {keys, sum};
+  }
+
+  test = testObjectBindingPatternLHSBlockStatement();
+  assertFalse(testDone);
+  assertEquals(
+      {keys: ['first', 'unknown', 'unknown', 'last'], sum: 10}, await test);
+  assertTrue(testDone);
+
+  async function testArrayBindingPatternLHSStatement() {
+    let sum = 0;
+    let keys = [];
+    let value;
+    let key;
+    let collection = [['first', 1], [undefined, 2], [, 3], ['last', 4]];
+    testDone = false;
+    for await ([key = 'unknown', value] of async(collection)) {
+      'use strict';
+      let strict = (function() { return this === undefined; })();
+      assertFalse(strict);
+      keys.push(key);
+      sum += value;
+    }
+    testDone = true;
+    return {keys, sum};
+  }
+
+  test = testArrayBindingPatternLHSStatement();
+  assertFalse(testDone);
+  assertEquals(
+      {keys: ['first', 'unknown', 'unknown', 'last'], sum: 10}, await test);
+  assertTrue(testDone);
+
+  async function testArrayBindingPatternLHSBlockStatement() {
+    let sum = 0;
+    let keys = [];
+    let value;
+    let key;
+    let collection = [
+      {key: 'first', value: 1}, {key: undefined, value: 2}, {value: 3},
+      {key: 'last', value: 4}
+    ];
+    testDone = false;
+    for await ({key = 'unknown', value} of async(collection)) {
+      'use strict';
+      let strict = (function() { return this === undefined; })();
+      assertFalse(strict);
+      keys.push(key);
+      sum += value;
+    }
+    testDone = true;
+    return {keys, sum};
+  }
+
+  test = testArrayBindingPatternLHSBlockStatement();
+  assertFalse(testDone);
+  assertEquals(
+      {keys: ['first', 'unknown', 'unknown', 'last'], sum: 10}, await test);
+  assertTrue(testDone);
+
+  // --------------------------------------------------------------------------
+
+  async function testBreakStatementReturnMethodNotPresent() {
+    let log = [];
+    let collection = [1, 2, 3, 4, 5];
+    let sum = 0;
+    let i = 0;
+    testDone = false;
+    for await (var x of async(collection, kNext, log)) {
+      sum += x;
+      if (++i === 3) break;
+    }
+    testDone = true;
+    return { sum, log };
+  }
+
+  test = testBreakStatementReturnMethodNotPresent();
+  assertFalse(testDone);
+  assertEquals({sum: 6, log: ['[Symbol.asyncIterator]()',
+                              '.next() -> resolved 1',
+                              '.next() -> resolved 2',
+                              '.next() -> resolved 3']},
+               await test);
+  assertTrue(testDone);
+
+  async function testBreakStatementReturnMethodPresent() {
+    let log = [];
+    let collection = [1, 2, 3, 4, 5];
+    let sum = 0;
+    let i = 0;
+    testDone = false;
+    for await (var x of async(collection, kNext|kReturn, log)) {
+      sum += x;
+      if (++i === 2) break;
+    }
+    testDone = true;
+    return { sum, log };
+  }
+
+  test = testBreakStatementReturnMethodPresent();
+  assertFalse(testDone);
+  assertEquals({sum: 3, log: ['[Symbol.asyncIterator]()',
+                              '.next() -> resolved 1',
+                              '.next() -> resolved 2',
+                              '.return(undefined)']},
+               await test);
+  assertTrue(testDone);
+
+  async function testReturnStatementReturnMethodNotPresent() {
+    let log = [];
+    let collection = [1, 2, 3, 4, 5];
+    let sum = 0;
+    let i = 0;
+    testDone = false;
+    for await (var x of async(collection, kNext, log)) {
+      sum += x;
+      if (++i === 3) {
+        testDone = true;
+        return { sum, log };
+      }
+    }
+  }
+
+  test = testReturnStatementReturnMethodNotPresent();
+  assertFalse(testDone);
+  assertEquals({sum: 6, log: ['[Symbol.asyncIterator]()',
+                              '.next() -> resolved 1',
+                              '.next() -> resolved 2',
+                              '.next() -> resolved 3']},
+               await test);
+  assertTrue(testDone);
+
+  async function testReturnStatementReturnMethodPresent() {
+    let log = [];
+    let collection = [1, 2, 3, 4, 5];
+    let sum = 0;
+    let i = 0;
+    testDone = false;
+    for await (var x of async(collection, kNext|kReturn, log)) {
+      sum += x;
+      if (++i === 2) {
+        testDone = true;
+        return { sum, log };
+      }
+    }
+  }
+
+  test = testReturnStatementReturnMethodPresent();
+  assertFalse(testDone);
+  assertEquals({sum: 3, log: ['[Symbol.asyncIterator]()',
+                              '.next() -> resolved 1',
+                              '.next() -> resolved 2',
+                              '.return(undefined)']},
+               await test);
+  assertTrue(testDone);
+
+  async function testThrowStatementReturnMethodNotPresent() {
+    let log = [];
+    let collection = [1, 2, 3, 4, 5];
+    let sum = 0;
+    let i = 0;
+    testDone = false;
+    for await (var x of async(collection, kNext|kThrow, log)) {
+      sum += x;
+      if (++i === 3) {
+        testDone = true;
+        throw { sum, log, toString() { return 'TestError'; } };
+      }
+    }
+    return { sum, log };
+  }
+
+  test = testThrowStatementReturnMethodNotPresent();
+  assertFalse(testDone);
+  try {
+    await test;
+    assertUnreachable('Awaited Promise should be rejected');
+  } catch (e) {
+    assertEquals('TestError', e.toString());
+    assertEquals(6, e.sum);
+    assertEquals(['[Symbol.asyncIterator]()', '.next() -> resolved 1',
+       '.next() -> resolved 2', '.next() -> resolved 3'
+      ], e.log);
+    assertTrue(testDone);
+  }
+
+  async function testThrowStatementReturnMethodPresent() {
+    let log = [];
+    let collection = [1, 2, 3, 4, 5];
+    let sum = 0;
+    let i = 0;
+    testDone = false;
+    for await (var x of async(collection, kNext|kThrow|kReturn, log)) {
+      sum += x;
+      if (++i === 2) {
+        testDone = true;
+        throw { sum, log, toString() { return 'TestError2'; } };
+      }
+    }
+    return { sum, log };
+  }
+
+  test = testThrowStatementReturnMethodPresent();
+  assertFalse(testDone);
+  try {
+    await test;
+    assertUnreachable('Awaited Promise should be rejected');
+  } catch (e) {
+    assertEquals('TestError2', e.toString());
+    assertEquals(3, e.sum);
+    assertEquals(['[Symbol.asyncIterator]()', '.next() -> resolved 1',
+       '.next() -> resolved 2', '.return(undefined)'
+      ], e.log);
+    assertTrue(testDone);
+  }
+
+})().then(undefined, function(error) {
+  testFailed = true;
+  testFailure = error;
+});
+
+%RunMicrotasks();
+
+if (testFailed) {
+  throw testFailure;
+}