Update variable value in module - node.js

Question

I'm a real newbie in node.js so pls understand my possible stupidity
I'm trying to use a external file to serve as a module so I can use it in other files. The project is bigger than this but let's say my module is:
var Tools = module.exports = {
result_arr: [],
object_data: {
times : [],
temps1 : [],
temps2 : [],
temps3 : [],
temps4 : [],
levels : [],
flows : []
},
getLastNRows: function (whereIsData, DB_info, table, NRows) {
if (whereIsData == "MySQL") {
function setValue (value) {
Tools.result_arr = value;
}
function dataArray2Object (array_data) {
Tools.object_data.times = array_data.map(row => row.timestamp);
Tools.object_data.temps1 = array_data.map(row => row.temp1);
Tools.object_data.temps2 = array_data.map(row => row.temp2);
Tools.object_data.temps3 = array_data.map(row => row.temp3);
Tools.object_data.temps4 = array_data.map(row => row.temp4);
Tools.object_data.levels = array_data.map(row => row.level_ice_bank);
Tools.object_data.flows = array_data.map(row => row.flow);
}
var queryString = "SELECT timestamp, temp1, temp2, temp3, temp4, level_ice_bank, flow FROM " +
table + " ORDER BY id DESC LIMIT " + NRows + ";";
var connnection = mysql.createConnection(DB_info);
connnection.connect(function(err) {
console.log("connected");
if (err) throw err;
});
connnection.query(queryString, function (err, rows) {
console.log("queried");
if (err) throw err;
setValue(rows);
dataArray2Object(Tools.result_arr);
console.log(Tools.result_arr);
console.log(Tools.object_data);
});
}
else {
console.log("Function only accepts data stored in MySQL.\n(u still have to improve...)");
return;
}
};
The variable object_data is supposed to be used in a main file. This way, whenever I call getLastNRows, I expect object_data to be updated by the operations in getLastNRows. The main file would be:
var tools = require('./tools');
var where2save = "MySQL";
var info_db = {
host : "127.0.0.1",
user : "root",
password: "xxxx",
database: "mydb",
port : 3306
};
var table = "tempdata";
var NRows = 4;
tools.getLastNRows(where2save, info_db, table, NRows);
console.log(tools.object_data);
What is observed is that, in fact, tools.object_data is not updated by getLastNRows in the main file, although console.log(Tools.object_data); from the tools.js (module) file logs the updated values. So my question is:
How can I make getLastNRows update tools.object_data (which is empty when created) in the main file?

Answer 1

Is getLastNRows asynchronous? Cuz it seems to me that is the cause of the problem.
It calls the getLastNRows in main which then calls connection.query, which gets put on a worker thread then immediately continues to the console.log where tools.object_data has not been updated.
Try:
getLastNRows: function (whereIsData, DB_info, table, NRows, cb) {
// ...
connnection.query(queryString, function (err, rows) {
console.log("queried");
if (err) throw err;
setValue(rows);
dataArray2Object(Tools.result_arr);
console.log(Tools.result_arr);
console.log(Tools.object_data);
cb()
});
// ...
}
// in main
tools.getLastNRows(where2save, info_db, table, NRows, function() {
console.log(tools.object_data);
});