core-js/internals/iterators-core.js

'use strict';
var fails = require('../internals/fails');
var isCallable = require('../internals/is-callable');
var isObject = require('../internals/is-object');
var create = require('../internals/object-create');
var getPrototypeOf = require('../internals/object-get-prototype-of');
var defineBuiltIn = require('../internals/define-built-in');
var wellKnownSymbol = require('../internals/well-known-symbol');
var IS_PURE = require('../internals/is-pure');

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

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

/* eslint-disable es/no-array-prototype-keys -- safe */
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;
  }
}

var NEW_ITERATOR_PROTOTYPE = !isObject(IteratorPrototype) || fails(function () {
  var test = {};
  // FF44- legacy iterators case
  return IteratorPrototype[ITERATOR].call(test) !== test;
});

if (NEW_ITERATOR_PROTOTYPE) IteratorPrototype = {};
else if (IS_PURE) IteratorPrototype = create(IteratorPrototype);

// `%IteratorPrototype%[@@iterator]()` method
// https://tc39.es/ecma262/#sec-%iteratorprototype%-@@iterator
if (!isCallable(IteratorPrototype[ITERATOR])) {
  defineBuiltIn(IteratorPrototype, ITERATOR, function () {
    return this;
  });
}

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