Error: can't set headers after they are sent.

this error happen when you send multiple response .

​

for example :-

​

​

var express = require('express');

var router = express.Router();

const Jwt= require('jsonwebtoken');

const jwtKey='e-comm'

​

/* GET login. */

let testName='test';

let testEmail='test@gmail.com';

router.get('/', function(req, res, next) {

    console.log("req",req.body)

const {name,email}=req.body;

    if(name==testName && email==testEmail){

        let token=Jwt.sign({name,email},jwtKey,{expiresIn:'1h'});

        res.json({                                      

            success:true,

            token

        })

    }

  res.send('login page');

});

​

module.exports = router;

​

in above example i send two types so i get error remove the last one response 

​

​

var express = require('express');

var router = express.Router();

const Jwt= require('jsonwebtoken');

const jwtKey='e-comm'

​

/* GET login. */

let testName='test';

let testEmail='test@gmail.com';

router.get('/', function(req, res, next) {

    console.log("req",req.body)

const {name,email}=req.body;

    if(name==testName && email==testEmail){

        let token=Jwt.sign({name,email},jwtKey,{expiresIn:'1h'});

        res.json({                                      

            success:true,

            token

        })

    }

});

​

module.exports = router;

app.get('/a', (req, res) => {

  res.send('Hello World!');

  // ⛔️ Calling send method twice

  res.send('Hello World!');

});

​

app.get('/b', (req, res) => {

  res.setHeader('Content-Type', 'application/json');

  res.send('Hello World!');

  // ⛔️ Setting headers after response has been sent

  res.setHeader('Content-Type', 'text/html');

});

​

app.get('/c', (req, res) => {

  // ⛔️ Using both send and redirect in a single request

  res.send('Hello World!!!');

  res.redirect('/articles');

});

HTTP uses a cycle that requires one response per request. When the client sends a request (e.g. POST or GET) the server should only send one response back to it.

​

This error message:

​

Error: Can't set headers after they are sent.

​

usually happens when you send several responses for one request. Make sure the following functions are called only once per request:

​

res.json()

res.send()

res.redirect()

res.render()

(and a few more that are rarely used, check the accepted answer)

​

The route callback will not return when these res functions are called. It will continue running until it hits the end of the function or a return statement. If you want to return when sending a response you can do it like so: return res.send().

​

​

const http = require('http');

​

const server = http.createServer((req, res) => {

  // Setting headers

  res.setHeader('Content-Type', 'text/plain');

​

  // Simulating some processing delay

  setTimeout(() => {

    // Sending the response

    res.statusCode = 200;

    res.end('Hello, world!');

  }, 1000);

});

​

// Start the server

server.listen(3000, () => {

  console.log('Server is running on port 3000');

});

if (req.body.password !== originalPassword) {

  res.status(401).json("Wrong credentials!");

  return;

}

HTTP uses a cycle that requires one response per request. When the client sends a request (e.g. POST or GET) the server should only send one response back to it.

​

This error message:

​

Error: Can't set headers after they are sent.

​

usually happens when you send several responses for one request. Make sure the following functions are called only once per request:

​

res.json()

res.send()

res.redirect()

res.render()

(and a few more that are rarely used, check the accepted answer)

​

The route callback will not return when these res functions are called. It will continue running until it hits the end of the function or a return statement. If you want to return when sending a response you can do it like so: return res.send().

​