nodejs getting db delayed result only works with console.log - node.js

Question

I'm aware of the event-driven/non-blocking stuff of node and I've been using it for about 2 years...
recently I came through this problem I can't solve it even forcing a closure...
I'm asking database for a simple result: 'SELECT 1+1 as theResult'
(...) // previous code
var dbRows1 = {}; // empty object to hold rows
var dbRows2 = {}; // idem
var mysql = require( 'mysql' );
var db = mysql.createConnection( dbInfo ); // dbInfo has connction data
var test = function( a ) { dbRows2 = a };
db.connect(
function( err )
{
if (err) throw err.stack;
console.log( 'TID ->', db.threadId)
});
db.query (
'SELECT 1+1 AS XXX',
function( err, rows, fields )
{
console.log( 'rows ->', rows ); // works ok
dbRows1 = rows; // don't work because rows is still empty
test( rows ); // !!!should work but dbRows2 is empty at program end!!!
});
(...) // more code
console.log( dbRows2 );
the last line prints a empty object for dbRows2 ( { } )...
Any ideas why console.log() works and my test() function do not work...

Answer 1

Your test function is working, the problem is that, at the time your last console.log statement executes, the test function hasn't been executed yet. This is because both .connect and .query are asynchronous.
The program flow looks something like this:
connect is called and queued
query is called and queued
console.log(dbRows2) is called
(time passes...)
connect succeeds and calls back
(time passes...)
query succeeds and calls back
test is called assigning rows to dbRows2
You can verify this behavior yourself by placing some strategic logging in your code before each action and inside of the callbacks. If you were to do that you would see something like this in your console:
about to call connect
about to call query
logging dbRows2
connect succeeded
query succeeded
about to call test
Without knowing the exact structure of your code, the following provides a rough example of how you might structure your logic to ensure the code that depends on the query completing is only invoked after the query completes:
db.query (
'SELECT 1+1 AS XXX',
function( err, rows, fields )
{
console.log( 'rows ->', rows ); // works ok
dbRows1 = rows; // don't work because rows is still empty
test( rows ); // !!!should work but dbRows2 is empty at program end!!!
// Call doStuffThatDependsOnQuery here
doStuffThatDependsOnQuery();
});
(...) // more code that doesn't depend on db.query(...)
function doStuffThatDependsOnQuery() {
console.log( dbRows2 );
}