I'm building a nodejs app using mongoose. I am trying to change a variable that is outside the mongoose findOne function, but, for some reason, it doesnt change that var.

    let existent_teams;

    match.findOne({ match_id: match_id }, (err, docs) => {
        if(err) console.error(err);

        var length = docs.match_teams.length; //Returns 0

        existent_teams = length; //Giving existent_teams var the length value
    });

    console.log(existent_teams); //Returns undefined

And it is returning me that the value of the variable existent_teams is undefined... I already tried changing the let to const and also to var