When I uncomment one line of code, I receive this error: _http_outgoing.js:359 throw new Error('Can\'t set headers after they are sent.');

Question

When I uncomment this line: return done(null, false, { message: \'Incorrect username\' }); in the following code, Node.js runs without any error, otherwise, Node.js

Answer 1

That error message is caused by a timing error in the handling of an async response that causes you to attempt to send data on a response after the response has already been sent.

It usually happens when people treat an async response inside an express route as a synchronous response and they end up sending data twice.

You should add else in your statement

if (password !== user.password) {
   return done(null, false, { message: 'Incorrect password' });
} else {
    return done(null, user);
}

Update:

function UserFind(username, cb) {
    var userFound = false, userVal = "";
    db.view('users/by_username', function(err, res) {
        if (err) {
            //db.view returned error
            return cb(err);
        }
        res.forEach(function(key, value, id) {
                //1st input=key|username, 2nd input=value|userDocument, 3rd input=id|_id
                //console.log('key: '+key+' row: '+row+' id: '+ id);
                if (username === key) {
                    //found the user
                    userFound = true;
                    userVal = value;
                }
            });

       if (userFound) {
          return cb(false, userVal);
       } else {
         // User did not found
         return cb(false, false);
       }
    })
}