Cannot use global variable in NodeJS MySQL

Question

I cannot access the upcoming_matches array inside the MySQL query callback, how come?

I'm greeted with a 'TypeError: Cannot read property '1' of null' error message on the console.log(upcoming_matches[1]); line which indicates that the variable is being reset for some reason (a guess, I'm not very experienced with Javascript)?

var regex = regex code..

while ((upcoming_matches = regex.exec(body)) != null) {
    HLTVID = upcoming_matches[1].split("-");    

    connection.query('SELECT * FROM `csgo_matches` WHERE HLTVID=' + HLTVID[0], function(err, rows, fields) {
        if (err) throw err;
        console.log(upcoming_matches[1]);
    });
}

score 4 · Accepted Answer · edited May 23 '17 at 12:05

4

Because at the moment the callback passed to connection.query is executed, the while loop already finished and upcoming_matches is null (because that's the condition for the while loop to stop).

connection.query is asynchronous.

See Why is my variable unaltered after I modify it inside of a function? - Asynchronous code reference

edited May 23 '17 at 12:05

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answered Dec 02 '14 at 00:33

Felix Kling

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Cannot use global variable in NodeJS MySQL

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