Why app.use(fn, '/api/auth', require('./routes/auth.routes')) errors?

Question

I'm new to Node.js. What is the error and how to fix it?Help me please Error code + below is my code:

app.use(fn, '/api/auth', require('./routes/auth.routes'))
ReferenceError: fn is not defined
at Object.<anonymous> (D:\Apps\app.js:6:9)
at Module._compile (module.js:653:30)
at Object.Module._extensions..js (module.js:664:10)
at Module.load (module.js:566:32)
at tryModuleLoad (module.js:506:12)
at Function.Module._load (module.js:498:3)
at Function.Module.runMain (module.js:694:10)
at startup (bootstrap_node.js:204:16)
at bootstrap_node.js:625:3



     const express = require('express')
     const config = require('config')
     const mongoose = require('mongoose')

     const app = express()
     app.use(fn, '/api/auth', require('./routes/auth.routes'))

     const PORT = config.get('port') || 5000

     async function start() {
         try{
            await mongoose.connect(config.get ('mongoUri'), {
                useNewUrlParser: true,
                useUnifiedTopology: true,
                useCreateIndex: true
            })
            app.listen(PORT, () => console.log('App worked'))
        } catch (e){
            console.log('Server Error', e.message)
            process.exit(code, 1)
        }
   }
   start()

Tried it app.use(fn: '/api/auth', require('./routes/auth.routes')), but it doesn't work

Answer 1

A proper call to app.use() takes a first optional argument that is a string which represents a path or a path prefix and then it takes any number of middleware function references after that. Doc reference for app.use() here .

So, what you are doing:

app.use(fn, '/api/auth', require('./routes/auth.routes'))

Is not a valid way to call app.use() and then on top of that, fn is not even defined which makes it a ReferenceError (won't even run).

I don't know where you got the idea to use the form you have, but it should probably be this:

app.use('/api/auth', require('./routes/auth.routes'))