Node.js JSON Encode – Array Output Is Empty - json

Question

I wroted this code to get a value from a database column to output with in JSON array. I succeeded to get it on the browser console, so I tried it with another value and used the same format to the code to passing it from my class file to the router app.post on the other file. I can see it on the terminal when I use console.log, but I can't see the output in the browser response, so what's wrong?
The code that successfully prints output:
auth.js, router part
app.post('/dispalymove', function (req, res, next) {
var lMove="";
if(req.body.MoveString !== null){
Move.setMoveUserId(req.user.id);
Move.setMoveString(req.body.MoveString);
lMove = a.getLastMove(req.user.GameId,function(move){
console.log("Return from display move:",move);
});
}
var output = {"msg":lMove, "loggedin":"true"};
res.send(JSON.stringify(output));
});
The function that I call on move.js file:
getLastMove(id,callback){
var MoveRequest = "SELECT * FROM users ORDER BY id";
var query = connection.query(MoveRequest, function(err,rows, result) {
if (rows.length == 0) {
return callback ("rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1");
}
if (rows.length > 0) {
for (var i in rows) {
var move = rows[i].MoveString;
if (rows[i].GameId == id){
callback(move);
}
}
}
});
var move="rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1";
return move;
}
The response on the browser console when the output is successful:
msg:"rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1"
loggedin:"true"
the outputting code that have the problem
app.post('/getcolor', function (req, res, next) {
var lCol="";
if(req.body.MoveString !== null){
Move.setMoveUserId(req.user.id);
lCol = a.getColor(req.user.id,function(col){
console.log("Return from getcolor:",col)
//the the value that i get on terminal "Return from getcolor:white"
});
}
var output = {"msg":lCol, "loggedin":"true"};
res.send(JSON.stringify(output));
});
The function that I call from the other file:
getColor(id,callback){
var ColRequest = "SELECT * FROM users ORDER BY id";
var query = connection.query(ColRequest, function(err,rows, result) {
if (rows.length == 0) {
return callback ("rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1");
}
if (rows.length > 0) {
for (var i in rows) {
var col = rows[i].GameColor;
if (rows[i].id == id){
callback(col);
}
}
}
});
var col="";
return callback(col);
}
The value that I get on my browser console response output just
loggedin:"true"
that should be like that
msg:"white"
loggedin:"true"
I tried to write this code with php
to post getcolor like that
session_start();
include "../classes/move.php";
$lCol="";
if(isset($_POST['MoveString'])){
$move = new move();
$move->setMoveUserId($_SESSION['UserId']);
$lCol=$move->getColor($_SESSION['UserId']);
}
$output = array("msg"=>"$lCol", "loggedin"=>"true");
echo json_encode($output);
and the function that i call
public function getColor($id){
include "../../connectToDB.php";
$ColRequest=$_db->query("SELECT * FROM users ORDER BY UserId");
$existCount = $ColRequest->rowCount();
if ($existCount == 0) { // evaluate the count
return "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1";
}
if ($existCount > 0) {
while($row = $ColRequest->fetch(PDO::FETCH_ASSOC)){
$userID = $row["UserId"];
$col = $row["GameColor"];
if($userID == $id) {
return $col;
}
}
}
$col="";
return $col;
}
and the output was that on browser console responses
msg:"white"
loggedin:"true"

Answer 1

This is because of lCol = a.getColor(req.user.id,function(col):
lCol is undefined here because getColor returns nothing, it expects a callback and gives you a value in this callback (while getLastMove in the contrary does return something). Try with :
app.post('/getcolor', function (req, res, next) {
var lCol = "";
if (req.body.MoveString !== null) {
Move.setMoveUserId(req.user.id);
// lCol = <=== useless because a.getcolor returns nothing
a.getColor(req.user.id, function (col) {
console.log("Return from getcolor:", col)
//the the value that i get on terminal "Return from getcolor:white"
res.json({"msg": col, "loggedin": "true"}); // <=== here you have a defined lCol
});
} else {
var output = {"msg": lCol, "loggedin": "true"}; // <=== here lCol always equals ""
res.json(output);
}
// var output = {"msg": lCol, "loggedin": "true"}; // <=== here lCol always equals undefined (when req.body.MoveString !== null)
// res.send(JSON.stringify(output));
});
Edit: in the getColor and getLastMove function you sould not return anthing: just use the callback: because connection.query is asynchronous any return will be invalid; In getColor your are doing
var col="";
return callback(col); so you will always have a "" response. Beware: do not call a callback function several times when it ends to a server response (you can't send multiple responses for one request): your callback calls are in a loop, they should not, just call it once.