drupal/core/modules/big_pipe/big_pipe.routing.yml

big_pipe.nojs:
  path: '/big_pipe/no-js'
  defaults:
    _controller: '\Drupal\big_pipe\Controller\BigPipeController:setNoJsCookie'
    _title: 'BigPipe no-JS check'
  options:
    no_cache: TRUE
  requirements:
    _access: 'TRUE'