How does one assign a NodeJS query to a global array variable?

Question

I am fairly new to Javascript and am currently working on a project using a MySQL server and NodeJS.

The problem I am having is that when I attempt to push the results of the MySQL query to a global array, the array comes back completely empty. Is there something I am doing wrong or some additional steps that someone can explain to me?

Relevant code:

var itemList = [];
var siteList = [];

function getItems(){
        con.connect(function(err) {
            try{
                if (err) throw err;
                    con.query("SELECT DISTINCT ProductURL FROM products;", function (err, result, fields) {
                if (err) throw err;
                    for (i=0; i<result.length; i++){
                        itemList.push(result[i].ProductURL);
                }
            });
            } finally{
                con.end();
            }
        });

async function another_function() {
 //Does some stuff with the information in the itemList array and inputs to siteList
}

async function anofuncV2() {
  //does more stuff with the information provided by another_function
}

let result = await getItems();
itemList.forEach(another_function);
anofuncV2(siteList);

The connection itself is fine and tested as well as a console.log right after the array push comes back with the correct information.

Additional note: I do need it as a global array for the other functions to work properly, I do know I could put it after the push to work, but that isn't what Im looking for

Edit 1: I understand that the code is asynchronous, but the entire concept of asynchronous code confuses me not matter how much I research it. So if someone could give a simple explanation that would be wonderful.

What I understand:

It runs at the same time as synchronous code causing the other code to run before the information can be input into the array

score 0 · Answer 1 · answered Jul 09 '21 at 17:42

That is how asyncronous code works in JavaScript.

Additional note: I do need it as a global array for the other functions to work properly, I do know I could put it after the push to work, but that isn't what Im looking for

You need to await the result from the getItems func and only proceed with the execution after it is executed.

Ideally, this is how it should be.

var itemList = [];

async function getItems(){
    return new Promise((resolve, reject) => {
        con.connect(function(err) {
            try {
                if (err) throw err;
                    con.query("SELECT DISTINCT ProductURL FROM products;", function (err, result, fields) {
                    if (err) throw err;
                        for (i=0; i<result.length; i++){
                            itemList.push(result[i].ProductURL);
                    }
                });
                resolve(itemList); 
            } finally {
                con.end();
                reject(undefined) // handle error
            }
        });
    })
}

let result = await getItems(); // this will print values inside of itemList array.

Unfortunately that solution didn't work with my code, but that may be my fault for not providing more information. I have edited the code above to more accurately outline the flow of the program. — Beanman, Jul 12 '21 at 15:15

How does one assign a NodeJS query to a global array variable?

1 Answers1