v8/test/mjsunit/harmony/array-flatMap.js

// Copyright 2018 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: --allow-natives-syntax

assertEquals(Array.prototype.flatMap.length, 1);
assertEquals(Array.prototype.flatMap.name, 'flatMap');

assertEquals(
  [1, 2, 3, 4].flatMap((element) => [element, element ** 2]),
  [1, 1, 2, 4, 3, 9, 4, 16]
);
assertEquals(
  [1, 2, 3, 4].flatMap((element) => [[element, element ** 2]]),
  [[1, 1], [2, 4], [3, 9], [4, 16]]
);

{
  const elements = new Set([
    -Infinity,
    -1,
    -0,
    +0,
    +1,
    Infinity,
    null,
    undefined,
    true,
    false,
    '',
    'foo',
    /./,
    [],
    {},
    Object.create(null),
    new Proxy({}, {}),
    Symbol(),
    x => x ** 2,
    String
  ]);

  for (const value of elements) {
    assertEquals(
      [value].flatMap((element) => [element, element]),
      [value, value]
    );
  }
}

{
  const array = [42];
  assertEquals(
    [array].flatMap((element) => [element, element]),
    [array, array]
  );
}

{
  const nonCallables = new Set([
    -Infinity,
    -1,
    -0,
    +0,
    +1,
    Infinity,
    null,
    undefined,
    true,
    false,
    '',
    'foo',
    /./,
    [],
    {},
    Object.create(null),
    new Proxy({}, {}),
    Symbol(),
  ]);
  for (const nonCallable of nonCallables) {
    assertThrows(() => {
      [].flatMap(nonCallable);
    }, TypeError);
  }
}

{
  const object = {
    foo: 42,
    get length() {
      object.foo = 0;
    }
  };
  const result = [object].flatMap((element) => [element, element]);
  %HeapObjectVerify(result);
  assertEquals(result, [object, object]);
  assertEquals(result[0].foo, 42);
}

assertThrows(() => {
  Array.prototype.flatMap.call(null, (element) => element);
}, TypeError);
assertThrows(() => {
  Array.prototype.flatMap.call(undefined, (element) => element);
}, TypeError);

assertEquals(
  Array.prototype.flatMap.call(
    {
      length: 1,
      0: 'a',
      1: 'b',
    },
    (element) => element
  ),
  ['a']
);
assertEquals(
  Array.prototype.flatMap.call(
    {
      length: 2,
      0: 'a',
      1: 'b',
    },
    (element) => element
  ),
  ['a', 'b']
);

{
  const result = [1, 2, 3].flatMap(function() {
    return [this];
  }, 'abc');
  assertEquals(true, result[0] == 'abc');
  assertEquals(true, result[1] == 'abc');
  assertEquals(true, result[2] == 'abc');
}

{
  const input = { 0: 'a', 1: 'b', 2: 'c', length: 'wat' };
  assertEquals(Array.prototype.flatMap.call(input, x => [x]), []);
}

{
  let count = 0;
  const input = {
    get length() { ++count; return 0; }
  };
  const result = Array.prototype.flatMap.call(input, x => [x]);
  assertEquals(count, 1);
}

{
  const descriptor = Object.getOwnPropertyDescriptor(
    Array.prototype,
    'flatMap'
  );
  assertEquals(descriptor.value, Array.prototype.flatMap);
  assertEquals(descriptor.writable, true);
  assertEquals(descriptor.enumerable, false);
  assertEquals(descriptor.configurable, true);
}