Node.js Express.js Mongoose 错误 [ERR_HTTP_HEADERS_SENT]：在将标头发送到客户端后无法设置标头

Question

I have this error and try evething, I read that 'return' can be one cause of the error and promise can be another one but as you can see in the code above none of this is missing in the code. In the console.log(docs) it returns the document correctly. can any one have some solution, tks

exports.databaseController = (req, res) => {
   const promise = Database.find({}).exec()

   promise
    .then(docs => {
      if (!docs) {
      throw new Error('docs not found')
     }
     console.log(docs)
     return res.status(200).json(docs)
     })
    .catch(err => {
    console.log(err)                      // not found
    return res.status(404).json({ err })  // return your error msg
  })
}

// app
const controllerDatabase = 
require('../controllers/database.controller')

module.exports = app => {
  app.use((req, res, next) => {
  res.header('Access-Control-Allow-Headers', 'x-access-token, 
       Origin, Content-Type, Accept')
  next()
 })

  app.get('/api/v1/database', 
     controllerDatabase.databaseController)
}

// server.js
require('./app/routes/database.routes')(app)

Answer 1

Remove the console.log . its will set the header that why you are calling 2nd time you got the error

 console.log(res.json(docs)) // remove

Or if you need to console.log do with direct docs

 console.log(docs)

Answer 2

You are already sending your response in console.log. Remove the following

console.log(res.json(docs));

and this error will go away. If you want to console log your docs do this:

console.log(docs);