core-js/internals/iterators-core.js

'use strict';
var getPrototypeOf = require('../internals/object-get-prototype-of');
var createNonEnumerableProperty = require('../internals/create-non-enumerable-property');
var has = require('../internals/has');
var wellKnownSymbol = require('../internals/well-known-symbol');
var IS_PURE = require('../internals/is-pure');

var ITERATOR = wellKnownSymbol('iterator');
var BUGGY_SAFARI_ITERATORS = false;

var returnThis = function () { return this; };

// `%IteratorPrototype%` object
// https://tc39.github.io/ecma262/#sec-%iteratorprototype%-object
var IteratorPrototype, PrototypeOfArrayIteratorPrototype, arrayIterator;

if ([].keys) {
  arrayIterator = [].keys();
  // Safari 8 has buggy iterators w/o `next`
  if (!('next' in arrayIterator)) BUGGY_SAFARI_ITERATORS = true;
  else {
    PrototypeOfArrayIteratorPrototype = getPrototypeOf(getPrototypeOf(arrayIterator));
    if (PrototypeOfArrayIteratorPrototype !== Object.prototype) IteratorPrototype = PrototypeOfArrayIteratorPrototype;
  }
}

if (IteratorPrototype == undefined) IteratorPrototype = {};

// 25.1.2.1.1 %IteratorPrototype%[@@iterator]()
if (!IS_PURE && !has(IteratorPrototype, ITERATOR)) {
  createNonEnumerableProperty(IteratorPrototype, ITERATOR, returnThis);
}

module.exports = {
  IteratorPrototype: IteratorPrototype,
  BUGGY_SAFARI_ITERATORS: BUGGY_SAFARI_ITERATORS
};