Node.JS / JavaScript Async Call back issue - node.js

Question

I am trying to accomplish the following (should be quite basic and I must be missing something trivial):
Call a function with string that has a select statement
Wait until the DB call completes and the rows (or json equivalent) is returned
Populate http object to return back
Here is code:
util.js
exports.execute = function( query){
if (connection) {
connection.query(query, function(err, rows, fields) {
if (err) throw err;
console.log("from Util - " + JSON.stringify(rows));
return JSON.stringify(rows);
});
}
};
repo.js
var q = "select * from xxx";
var response;
util.execute(q, function (err, r){
if (err){
throw err;
console.log(err);
}
else {
console.log(r);
res.contentType('application/json');
res.write(r);
res.end();
}
});
My problem is while the code within util.js is called and I can see the json in console, it never comes back to the anonymous call back function in the repo.js.
What am I doing wrong here ?
Update
Thanks Ben
I also found the solution in same line ... here is new code:
repo.js:
var send_data = function (req, res, r){
res.contentType('application/json');
res.write(r);
res.end();
}
exports.all = function(req, res){
var q = "select * from XXX";
var response;
util.execute(req, res,q, send_data);
};
util.js:
exports.execute = function(req, res, query, callback){
if (connection) {
connection.query(query, function(err, rows, fields) {
if (err) throw err;
callback(req, res, JSON.stringify(rows)) ;
});
}
};

Answer 1

util.execute only accepts one parameter in your code. It needs to accept a second callback parameter in order to use it the way you do. (Callbacks aren't magic, they're just function calls)
Something like:
exports.execute = function(query,callback){
if (connection) {
connection.query(query, function(err, rows, fields) {
if (err) throw err;
console.log("from Util - " + JSON.stringify(rows));
callback(null,JSON.stringify(rows));
});
}
};
If you'd like it to behave consistently and accept an error parameter, you might want fill that in:
exports.execute = function(query,callback){
if (connection) {
connection.query(query, function(err, rows, fields) {
callback(err,null);
console.log("from Util - " + JSON.stringify(rows));
callback(null,JSON.stringify(rows));
});
}
};