Error Blog
This blog is about the error Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the client
Problem Statement
unable to start node js express application
Error Details
error Log
ERROR DETAILS
\node_modules\mysql\lib\protocol\Parser.js:437
throw err; // Rethrow non-MySQL errors
^
Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the client
at ServerResponse.setHeader (_http_outgoing.js:470:11)
at ServerResponse.header (F:\ \study\gitRepo\new\learn\nodejs\expressjs\node_modules\express\lib\response.js:771:10)
at ServerResponse.send (F:\ \study\gitRepo\new\learn\nodejs\expressjs\node_modules\express\lib\response.js:170:12)
at ServerResponse.json (F:\ \study\gitRepo\new\learn\nodejs\expressjs\node_modules\express\lib\response.js:267:15)
at F:\ \study\gitRepo\new\learn\nodejs\expressjs\service\users.js:24:11
at Query.<anonymous> (F:\ \study\gitRepo\new\learn\nodejs\expressjs\service\task.service.js:20:21)
at Query.<anonymous> (F:\ \study\gitRepo\new\learn\nodejs\expressjs\node_modules\mysql\lib\Connection.js:526:10)
at Query._callback (F:\ \study\gitRepo\new\learn\nodejs\expressjs\node_modules\mysql\lib\Connection.js:488:16)
at Query.Sequence.end (F:\ \study\gitRepo\new\learn\nodejs\expressjs\node_modules\mysql\lib\protocol\sequences\Sequence.js:83:24)
at Query._handleFinalResultPacket (F:\ \study\gitRepo\new\learn\nodejs\expressjs\node_modules\mysql\lib\protocol\sequences\Query.js:149:8)
Error Code
You will face this error if you res.send twice in an express js application.
var express = require('express');
var router = express.Router();
var Task = require('./task.service.js');
router.get('/', function(req, res){
Task.getAllTask(function(err, task) {
console.log('controller')
if (err)
res.send(err);
console.log('res', task);
res.send(task);
});
});
router.post('/create', function(req, res){
console.log(req.body);
var new_task = new Task(req.body);
console.log(new_task);
Task.createTask(new_task, function(err, task) {
if (err)
res.send(err);
res.json(task);
});
res.send('success.');
});
//export this router to use in our index.js
module.exports = router;
Solution
change the code so that res.send is not called twice . .
Code Changes
add the following import in your component.ts file .
if (err)
res.send(err);
res.json(task);
});
// res.send('success.');
OUTPUT
works
Thanks for reading . Let me know your thoughts in the comments below .
