mine/node_modules/core-js/modules/esnext.iterator.constructor.js

'use strict';
var $ = require('../internals/export');
var global = require('../internals/global');
var anInstance = require('../internals/an-instance');
var isCallable = require('../internals/is-callable');
var getPrototypeOf = require('../internals/object-get-prototype-of');
var createNonEnumerableProperty = require('../internals/create-non-enumerable-property');
var fails = require('../internals/fails');
var hasOwn = require('../internals/has-own-property');
var wellKnownSymbol = require('../internals/well-known-symbol');
var IteratorPrototype = require('../internals/iterators-core').IteratorPrototype;
var IS_PURE = require('../internals/is-pure');

var TO_STRING_TAG = wellKnownSymbol('toStringTag');

var $TypeError = TypeError;
var NativeIterator = global.Iterator;

// FF56- have non-standard global helper `Iterator`
var FORCED = IS_PURE
  || !isCallable(NativeIterator)
  || NativeIterator.prototype !== IteratorPrototype
  // FF44- non-standard `Iterator` passes previous tests
  || !fails(function () { NativeIterator({}); });

var IteratorConstructor = function Iterator() {
  anInstance(this, IteratorPrototype);
  if (getPrototypeOf(this) === IteratorPrototype) throw $TypeError('Abstract class Iterator not directly constructable');
};

if (!hasOwn(IteratorPrototype, TO_STRING_TAG)) {
  createNonEnumerableProperty(IteratorPrototype, TO_STRING_TAG, 'Iterator');
}

if (FORCED || !hasOwn(IteratorPrototype, 'constructor') || IteratorPrototype.constructor === Object) {
  createNonEnumerableProperty(IteratorPrototype, 'constructor', IteratorConstructor);
}

IteratorConstructor.prototype = IteratorPrototype;

// `Iterator` constructor
// https://github.com/tc39/proposal-iterator-helpers
$({ global: true, constructor: true, forced: FORCED }, {
  Iterator: IteratorConstructor
});