code: function copyFields(source: Record, sink: Record): void {
    for (const key in source) {
      if (source.hasOwnProperty(key)) {
        if (key !== ID_KEY && key !== TYPENAME_KEY) {
          sink[key] = source[key];
        }
      }
    }
  }
docs: @public
  
  Copies all fields from `source` to `sink`, excluding `__id` and `__typename`.
  
  NOTE: This function does not treat `id` specially. To preserve the id,
  manually reset it after calling this function. Also note that values are
  copied by reference and not value; callers should ensure that values are
  copied on write.