Nuxt/test/fixtures/module/modules/middleware/index.js

module.exports = function middlewareModule(options) {
  return new Promise((resolve, reject) => {
    // Add /api endpoint
    this.addServerMiddleware({
      path: '/api',
      handler(req, res, next) {
        res.end('It works!')
      }
    })
    // Add local middleware js
    this.addServerMiddleware('~/modules/middleware/log.js')
    // Add plain middleware
    this.addServerMiddleware((req, res, next) => {
      res.setHeader('x-nuxt', 'hello')
      next()
    })
    // Add file middleware
    this.addServerMiddleware('~/modules/middleware/midd1')
    resolve()
  })
}