node.js 标识符“express”已经声明

Question

I am new with node.js , this is the first project that I am testing to execute, and I have an issue. I review and comment and delete express but it is not solving.

const express = require('express');
const app = express();
require('dotenv').config()
const mongoose = require('mongoose')
const dadosRouter = require('./routes/data')

mongoose.connect(process.env.MONGO, { useNewUrlParser: true })
const db = mongoose.connection
db.on('error', (error) => console.error(error))
db.once('open', () => console.log('Conecting db'))

app.use(express.json())

app.set("view engine", "ejs");
app.use(express.urlencoded({ extended: false}))


app.use('/data', dataRouter)

app.get('/', (req, res) => {
  res.send("Opening")
})

app.listen(port, ()=> {
  console.log(`Rodando servidor pelo localhost $(3000)`)
});
app.listen(3000, () => console.log('Server started')) 

I have this error

const express = require('express')
  ^

SyntaxError: Identifier 'express' has already been declared

Answer 1

Issue is you are calling the server twice.

// Remove this
app.listen(port, ()=> {
  console.log(`Rodando servidor pelo localhost $(3000)`)
});