core-js/modules/es.string.iterator.js

'use strict';
var charAt = require('../internals/string-multibyte').charAt;
var InternalStateModule = require('../internals/internal-state');
var defineIterator = require('../internals/define-iterator');

var STRING_ITERATOR = 'String Iterator';
var setInternalState = InternalStateModule.set;
var getInternalState = InternalStateModule.getterFor(STRING_ITERATOR);

// `String.prototype[@@iterator]` method
// https://tc39.es/ecma262/#sec-string.prototype-@@iterator
defineIterator(String, 'String', function (iterated) {
  setInternalState(this, {
    type: STRING_ITERATOR,
    string: String(iterated),
    index: 0
  });
// `%StringIteratorPrototype%.next` method
// https://tc39.es/ecma262/#sec-%stringiteratorprototype%.next
}, function next() {
  var state = getInternalState(this);
  var string = state.string;
  var index = state.index;
  var point;
  if (index >= string.length) return { value: undefined, done: true };
  point = charAt(string, index);
  state.index += point.length;
  return { value: point, done: false };
});