Implement Symbol.Iterator for objects

ObjectIterators.js

/**
 * Apply to Symbol.iterator on object to enable iteration
 * 
 * @param field values, keys, entries
 * 
 * @return {Function}
 */
function ObjectIteraror(field) {
  if (!['keys', 'values', 'entries'].includes(field)) {
    throw new Error('Incorrect field value, available values: keys, values, entries');
  }

  return function() {
    return {
      _entries: Object[field](this),
      _currentIndex: 0,

      next() {
        const value = this._entries[this._currentIndex];
        const done = this._currentIndex === this._entries.length;

        this._currentIndex += 1;

        return { value, done };
      },
    };
  }
}

const ObjectIteratorValues = ObjectIteraror('values');
const ObjectIteratorKeys = ObjectIteraror('keys');
const ObjectIteratorEntries = ObjectIteraror('entries');

export {
  ObjectIteraror,
  ObjectIteratorKeys,
  ObjectIteratorValues,
  ObjectIteratorEntries,
};