nullish-coalescing.js

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var BUGNUMBER = 1566141;

var summary = "Implement the Nullish Coalescing operator (??) proposal";

print(BUGNUMBER + ": " + summary);

// These tests are originally from webkit.

// webkit specifics have been removed and a test for `document.all` has

// been added.

function shouldBe(actual, expected) {

  if (actual !== expected)

    throw new Error(`expected ${expected} but got ${actual}`);

function shouldNotThrow(script) {

  eval(script);

function shouldThrowSyntaxError(script) {

  let error;

  try {

    eval(script);

  } catch (e) {

    error = e;

  if (!(error instanceof SyntaxError))

    throw new Error('Expected SyntaxError!');

function testBasicCases() {

  shouldBe(undefined ?? 3, 3);

  shouldBe(null ?? 3, 3);

  shouldBe(true ?? 3, true);

  shouldBe(false ?? 3, false);

  shouldBe(0 ?? 3, 0);

  shouldBe(1 ?? 3, 1);

  shouldBe('' ?? 3, '');

  shouldBe('hi' ?? 3, 'hi');

  shouldBe(({} ?? 3) instanceof Object, true);

  shouldBe(({ x: 'hi' } ?? 3).x, 'hi');

  shouldBe(([] ?? 3) instanceof Array, true);

  shouldBe((['hi'] ?? 3)[0], 'hi');

  // test document.all, which has odd behavior

  shouldBe(typeof(createIsHTMLDDA() ?? 3), "undefined");

for (let i = 0; i < 1e5; i++)

  testBasicCases();

shouldBe(1 | null ?? 3, 1);

shouldBe(1 ^ null ?? 3, 1);

shouldBe(1 & null ?? 3, 0);

shouldBe(3 == null ?? 3, false);

shouldBe(3 != null ?? 3, true);

shouldBe(3 === null ?? 3, false);

shouldBe(3 !== null ?? 3, true);

shouldBe(1 < null ?? 3, false);

shouldBe(1 > null ?? 3, true);

shouldBe(1 <= null ?? 3, false);

shouldBe(1 >= null ?? 3, true);

shouldBe(1 << null ?? 3, 1);

shouldBe(1 >> null ?? 3, 1);

shouldBe(1 >>> null ?? 3, 1);

shouldBe(1 + null ?? 3, 1);

shouldBe(1 - null ?? 3, 1);

shouldBe(1 * null ?? 3, 0);

shouldBe(1 / null ?? 3, Infinity);

shouldBe(isNaN(1 % null ?? 3), true);

shouldBe(1 ** null ?? 3, 1);

shouldBe((void 0) ?? 3, 3);

const obj = {

      count: 0,

          get x() { this.count++; return 'x'; }

};

false ?? obj.x;

shouldBe(obj.count, 0);

null ?? obj.x;

shouldBe(obj.count, 1);

obj.x ?? obj.x;

shouldBe(obj.count, 2);

shouldThrowSyntaxError('0 || 1 ?? 2');

shouldThrowSyntaxError('0 && 1 ?? 2');

shouldThrowSyntaxError('0 ?? 1 || 2');

shouldThrowSyntaxError('0 ?? 1 && 2');

shouldNotThrow('(0 || 1) ?? 2');

shouldNotThrow('0 || (1 ?? 2)');

shouldNotThrow('(0 && 1) ?? 2');

shouldNotThrow('0 && (1 ?? 2)');

shouldNotThrow('(0 ?? 1) || 2');

shouldNotThrow('0 ?? (1 || 2)');

shouldNotThrow('(0 ?? 1) && 2');

shouldNotThrow('0 ?? (1 && 2)');

shouldNotThrow('0 || 1 && 2 | 3 ^ 4 & 5 == 6 != 7 === 8 !== 9 < 0 > 1 <= 2 >= 3 << 4 >> 5 >>> 6 + 7 - 8 * 9 / 0 % 1 ** 2');

shouldThrowSyntaxError('0 || 1 && 2 | 3 ^ 4 & 5 == 6 != 7 === 8 !== 9 < 0 > 1 <= 2 >= 3 << 4 >> 5 >>> 6 + 7 - 8 * 9 / 0 % 1 ** 2 ?? 3');

shouldThrowSyntaxError('3 ?? 2 ** 1 % 0 / 9 * 8 - 7 + 6 >>> 5 >> 4 << 3 >= 2 <= 1 > 0 < 9 !== 8 === 7 != 6 == 5 & 4 ^ 3 | 2 && 1 || 0');

shouldBe(null?.x ?? 3, 3);

shouldBe(({})?.x ?? 3, 3);

shouldBe(({ x: 0 })?.x ?? 3, 0);

shouldBe(null?.() ?? 3, 3);

shouldBe((() => 0)?.() ?? 3, 0);

shouldBe(({ x: 0 })?.[null?.a ?? 'x'] ?? 3, 0);

shouldBe((() => 0)?.(null?.a ?? 'x') ?? 3, 0);

if (typeof reportCompare === "function")

  reportCompare(true, true);

print("Tests complete");