Node.js returning result from MySQL query

Solution 1:

You have to do the processing on the results from the db query on a callback only. Just like.

function getColour(username, roomCount, callback)
{
    connection.query('SELECT hexcode FROM colours WHERE precedence = ?', [roomCount], function(err, result)
    {
        if (err) 
            callback(err,null);
        else
            callback(null,result[0].hexcode);

    });

}

//call Fn for db query with callback
getColour("yourname",4, function(err,data){
        if (err) {
            // error handling code goes here
            console.log("ERROR : ",err);            
        } else {            
            // code to execute on data retrieval
            console.log("result from db is : ",data);   
        }    

});

Solution 2:

If you want to use promises to avoid the so-called "callback hell" there are various approaches.

Here's an example using native promises and the standard MySQL package.

const mysql = require("mysql");

//left here for testing purposes, although there is only one colour in DB
const connection = mysql.createConnection({
  host: "remotemysql.com",
  user: "aKlLAqAfXH",
  password: "PZKuFVGRQD",
  database: "aKlLAqAfXH"
});

(async () => {
  connection.connect();
  const result = await getColour("username", 2);
  console.log(result);
  connection.end();
})();

function getColour(username, roomCount) {
  return new Promise((resolve, reject) => {
    connection.query(
      "SELECT hexcode FROM colours WHERE precedence = ?",
      [roomCount],
      (err, result) => {
        return err ? reject(err) : resolve(result[0].hexcode);
      }
    );
  });
}

In async functions, you are able to use the await expression which will pause the function execution until a Promise is resolved or rejected. This way the getColour function will return a promise with the MySQL query which will pause the main function execution until the result is returned or a query error is thrown.

A similar but maybe more flexible approach might be using a promise wrapper package of the MySQL library or even a promise-based ORM.