Error [ERR_STREAM_WRITE_AFTER_END]: write after end, http server node.js

Question

Setting up a new http server with Node.js

When you first launch it, it displays the proper html text on the screen but when you move to other links in my code ie: localhost:5001/about, it gives me an error in my IDE console

events.js:377
      throw er; // Unhandled 'error' event
      ^

Error [ERR_STREAM_WRITE_AFTER_END]: write after end
    at new NodeError (internal/errors.js:322:7)
    at writeAfterEnd (_http_outgoing.js:694:15)
    at ServerResponse.end (_http_outgoing.js:815:7)
    at Server.<anonymous> (/Users/angelo/Documents/coding/node/node-tutorial/app.js:11:7)
    at Server.emit (events.js:400:28)
    at parserOnIncoming (_http_server.js:900:12)
    at HTTPParser.parserOnHeadersComplete (_http_common.js:127:17)
Emitted 'error' event on ServerResponse instance at:
    at writeAfterEndNT (_http_outgoing.js:753:7)
    at processTicksAndRejections (internal/process/task_queues.js:83:21) {
  code: 'ERR_STREAM_WRITE_AFTER_END'
}
[nodemon] app crashed - waiting for file changes before starting...

app.js

const http = require('http');

const PORT = 5001;
const server = http.createServer((req, res) => {
  if(req.url === '/'){
    res.end('Home Page')
  }
  if(req.url === '/about'){
    res.end('About Page')
  }
  res.end('Error page')
})

server.listen(PORT, () => {
  console.log(`Server is listening on port: ${PORT}`)
})

I've been looking for answer for the 'write after end' error but have not seen this specific issue for this specific block of code

Answer 1

As mentioned on the comments, this is due to res.end being called multiple times, the simplest solution for you would either to return after each res.end or adjust your conditions:

const http = require('http');

const PORT = 5001;
const server = http.createServer((req, res) => {
  if(req.url === '/'){
    res.end('Home Page')
  }
  else if(req.url === '/about'){
    res.end('About Page')
  }
  else {
    res.end('Error page')
  }
})

server.listen(PORT, () => {
  console.log(`Server is listening on port: ${PORT}`)
})