promise-constructor-detection.js

var global = require('../internals/global');
var NativePromiseConstructor = require('../internals/promise-native-constructor');
var isCallable = require('../internals/is-callable');
var isForced = require('../internals/is-forced');
var inspectSource = require('../internals/inspect-source');
var wellKnownSymbol = require('../internals/well-known-symbol');
var IS_BROWSER = require('../internals/engine-is-browser');
var IS_DENO = require('../internals/engine-is-deno');
var IS_PURE = require('../internals/is-pure');
var V8_VERSION = require('../internals/engine-v8-version');

var NativePromisePrototype = NativePromiseConstructor && NativePromiseConstructor.prototype;
var SPECIES = wellKnownSymbol('species');
var SUBCLASSING = false;
var NATIVE_PROMISE_REJECTION_EVENT = isCallable(global.PromiseRejectionEvent);

var FORCED_PROMISE_CONSTRUCTOR = isForced('Promise', function () {
  var PROMISE_CONSTRUCTOR_SOURCE = inspectSource(NativePromiseConstructor);
  var GLOBAL_CORE_JS_PROMISE = PROMISE_CONSTRUCTOR_SOURCE !== String(NativePromiseConstructor);
  // V8 6.6 (Node 10 and Chrome 66) have a bug with resolving custom thenables
  // https://bugs.chromium.org/p/chromium/issues/detail?id=830565
  // We can't detect it synchronously, so just check versions
  if (!GLOBAL_CORE_JS_PROMISE && V8_VERSION === 66) return true;
  // We need Promise#{ catch, finally } in the pure version for preventing prototype pollution
  if (IS_PURE && !(NativePromisePrototype['catch'] && NativePromisePrototype['finally'])) return true;
  // We can't use @@species feature detection in V8 since it causes
  // deoptimization and performance degradation
  // https://github.com/zloirock/core-js/issues/679
  if (V8_VERSION < 51 || !/native code/.test(PROMISE_CONSTRUCTOR_SOURCE)) {
    // Detect correctness of subclassing with @@species support
    var promise = new NativePromiseConstructor(function (resolve) { resolve(1); });
    var FakePromise = function (exec) {
      exec(function () { /* empty */ }, function () { /* empty */ });
    };
    var constructor = promise.constructor = {};
    constructor[SPECIES] = FakePromise;
    SUBCLASSING = promise.then(function () { /* empty */ }) instanceof FakePromise;
    if (!SUBCLASSING) return true;
  // Unhandled rejections tracking support, NodeJS Promise without it fails @@species test
  } return !GLOBAL_CORE_JS_PROMISE && (IS_BROWSER || IS_DENO) && !NATIVE_PROMISE_REJECTION_EVENT;
});

module.exports = {
  CONSTRUCTOR: FORCED_PROMISE_CONSTRUCTOR,
  REJECTION_EVENT: NATIVE_PROMISE_REJECTION_EVENT,
  SUBCLASSING: SUBCLASSING
};