Best way to output SQLite data to JSON file

I'm trying to output code from an SQLite3 database with Javascript and Node.js, it selects the correct data and outputs each row to the console but doesn't add it to a JSON file using the code below:

var obj;  
db.serialize(function(){
    req = sqlRequest;
    console.log(req); //sql request to console
    db.each(req, function(err, row){
        console.log(row); //outputs every entry correctly
        obj += row;
    });

    db.close();
});
console.log(JSON.stringify(obj));
fs.writeFile(sqlRequest, JSON.stringify(obj), function(err){
    if(err){
        return console.log(err);
    }
    else
    {
        console.log("Json saved to: " + sqlRequest);
    }

    console.log("The file is saved");
});   

Any suggestions?