Cannot set headers after they are sent to clients in node.js - node.js

Question

My code is not working . I am beginner and don't know my problem. Kindly help.I have seen one or two solution on stackoverflow but didnot get .
This is code.
app.post('/post',(request,response)=>{
var description=request.body.description;
var contact_number=request.body.contact_number;
var city=request.body.city;
var budget=request.body.budget;
var category=request.body.optradio;
var query=connection.query("insert into jobs(Jobs_id,Description,Category,City,Contact_number,Budget) values(?,?,?,?,?,?)",[null,description,category,city,contact_number,budget],function(err){
if(err)
console.log(err);
else
response.send("successful");
});
response.redirect('/data');
});
app.get('/data',function(request,response){
connection.query("SELECT * FROM jobs ORDER BY Jobs_id DESC",(err, rows,fields) => {
if(err) {
console.log(err);
}
else {
response.render('feed', {title : 'Jobs Details',
items: rows })
}
});
});
app.listen(3000);
This is the error

Answer 1

pp.post('/post', (request, response) => {
var description = request.body.description;
var contact_number = request.body.contact_number;
var city = request.body.city;
var budget = request.body.budget;
var category = request.body.optradio;
var query = connection.query("insert into jobs(Jobs_id,Description,Category,City,Contact_number,Budget) values(?,?,?,?,?,?)", [null, description, category, city, contact_number, budget],
function (err) {
if (err) {
console.log(err);
} else {
response.redirect('/data');
}
});
});
app.get('/data', function (request, response) {
connection.query("SELECT * FROM jobs ORDER BY Jobs_id DESC", (err, rows, fields) => {
if (err) {
console.log(err);
}
else {
response.render('feed', {
title: 'Jobs Details',
items: rows
})
}
});
});
app.listen(3000);

Answer 2

There can be only one response to single HTTP request. In your code, you are first trying to send response with
response.send("successful");
but this on its own doesn't break the flow of the function which means that if the condition is actually met then this will execute and the execution continues and finds another response, in this case
response.redirect('/data');
and it will try to send another response to the original http request but at this point it is already too late because one response has already been send.
To solve this issue in general, you can place return in front of any line of code that is closing the the connection (response.send, response.redirect, ...). That way, the function's execution is terminated at the first response, whichever it is.
So you could do something like
var query=connection.query("insert into jobs(Jobs_id,Description,Category,City,Contact_number,Budget) values(?,?,?,?,?,?)",[null,description,category,city,contact_number,budget],function(err){
if(err)
console.log(err);
else
return response.send("successful");
});
return response.redirect('/data');
});