JavaScript Callbacks and Promises: Exploring Asynchronous Programming

Question

JavaScript Callbacks and Promises: Exploring Asynchronous Programming

For the past 2 days, I've been struggling to figure out my mistake. It seems that I can't get past the "undefined" returned value because I'm having trouble grasping callbacks or promises. Despite reading numerous posts and trying simple examples, I just can't seem to apply it to my own code...

function realloot(data){
    return data;
    console.log(`${data}`);
    }
 
 
function lootbox_openning(callback, user, type, nombre){
 
let sqlQueryopenbox = `SELECT item_qty FROM users_items WHERE discord_id = '${user}' AND item_id = ${type};`
 
let token_won=0;
let real_token_won=0;
let common_pp_looted = 0;
let rare_pp_looted = 0;
let epic_pp_looted = 0;
 
        db.query(sqlQueryopenbox, (err, rows) => {
            
            let user_box_real_qty = rows[0].item_qty;
            let sql;
        
            if (err) {
                real_token_won="sql error";
                throw err;
                }
                
            if (nombre > user_box_real_qty){real_token_won="error number";}
            
            else {
                //function open
                
                if (type==1) { 
                
                    for (var i = 0; i <= nombre; i++){
                        token_won=little_box_open();
                        real_token_won=real_token_won+token_won;
                    }
                    var myreturn = callback(real_token_won);
                    console.log(`${myreturn}`);
                    return myreturn;
                }
                if (type==2) {}
                if (type==3) {}
            }
        
        });
 
}
 
 
//this is a bot discord so huge on.message here...
 
 
 
            case "open":
                if (!args[1]) return message.channel.send('please give value box | bigbox');
                
                if (args[1] ==='box' ){
                    if (!args[2]) {message.channel.send ("Specify number please");}
                    if (args[2]) {
                        var number = parseInt(args[2]);
                        if (Number.isInteger(number)){
                            message.channel.send ("You re openning "+args[2]+" boxes");
                            **var token_won = lootbox_openning(realloot, message.author.id, 1, args[2]);** //PROBLEM IS HERE 
                            if (token_won==="error number"){message.channel.send ("Vous n'avez pas assez de box !");}
                            else {message.channel.send ("you won : "+token_won+" tokens !");}
                            }
                        else message.channel.send ("Give a valid number");
                        }
                    }

I've hit a wall with this problem and despite all my efforts, I still need more clarity and explanations...

javascript sql promise callback

Answer 1

Answer №1

Understanding asynchronous logic can be challenging for newcomers, but it essentially comes down to this:

Let's look at the difference between synchronous and asynchronous code:

function doQuery(id) {
  let res = db.query(`SELECT * FROM table WHERE id=${id}`)
  return res
}

With asynchronous code:

function doQuery(id, callback) {
  db.query(`SELECT * FROM table WHERE id=${id}`, function(res) {
    callback(res)
  })
}

The key difference is that instead of using return res, you need to use callback(res). This pattern is essential when dealing with asynchronous operations.

Once you venture into the world of async programming, there's no turning back to synchronous methods. For instance, attempting to mix sync and async logic like this is not feasible:

// some sync logic
let resultOfAsyncOperation = someAsyncFunction()
// some sync logic

When working with callbacks, everything needs to follow an async flow. The only exception is if you simply want a task to be executed without worrying about the timing or return value.

Applying these principles to your specific code snippet reveals a common issue - mixing async functions in synchronous logic.

var number = parseInt(args[2]);
if (Number.isInteger(number)) {
    message.channel.send("You're opening " + args[2] + " boxes"); **
    var token_won = lootbox_opening(realloot, message.author.id, 1, args[2]); ** //PROBLEM OCCURS HERE 
    if (token_won === "error number") {
        message.channel.send("Not enough boxes!");
    } else {
        message.channel.send("you won: " + token_won + " tokens!");
    }
} else message.channel.send("Provide a valid number");

To resolve this issue, you'll also need to convert this portion of code to be asynchronous:

message.channel.send("You're opening " + args[2] + " boxes");
function callback(token_won) {
  realloot(token_won)
  if (token_won === "error number") {
    message.channel.send("Not enough boxes!");
  } else {
    message.channel.send("you won: " + token_won + " tokens!");
  }
}
lootbox_opening(callback, message.author.id, 1, args[2]);

(Keep in mind that this example may need adjustments based on your specific requirements, but it illustrates the concept of transitioning to async practices)

Answer 2

Understanding asynchronous logic can be challenging for newcomers, but it essentially comes down to this:

Let's look at the difference between synchronous and asynchronous code:

function doQuery(id) {
  let res = db.query(`SELECT * FROM table WHERE id=${id}`)
  return res
}

With asynchronous code:

function doQuery(id, callback) {
  db.query(`SELECT * FROM table WHERE id=${id}`, function(res) {
    callback(res)
  })
}

The key difference is that instead of using return res, you need to use callback(res). This pattern is essential when dealing with asynchronous operations.

Once you venture into the world of async programming, there's no turning back to synchronous methods. For instance, attempting to mix sync and async logic like this is not feasible:

// some sync logic
let resultOfAsyncOperation = someAsyncFunction()
// some sync logic

When working with callbacks, everything needs to follow an async flow. The only exception is if you simply want a task to be executed without worrying about the timing or return value.

Applying these principles to your specific code snippet reveals a common issue - mixing async functions in synchronous logic.

var number = parseInt(args[2]);
if (Number.isInteger(number)) {
    message.channel.send("You're opening " + args[2] + " boxes"); **
    var token_won = lootbox_opening(realloot, message.author.id, 1, args[2]); ** //PROBLEM OCCURS HERE 
    if (token_won === "error number") {
        message.channel.send("Not enough boxes!");
    } else {
        message.channel.send("you won: " + token_won + " tokens!");
    }
} else message.channel.send("Provide a valid number");

To resolve this issue, you'll also need to convert this portion of code to be asynchronous:

message.channel.send("You're opening " + args[2] + " boxes");
function callback(token_won) {
  realloot(token_won)
  if (token_won === "error number") {
    message.channel.send("Not enough boxes!");
  } else {
    message.channel.send("you won: " + token_won + " tokens!");
  }
}
lootbox_opening(callback, message.author.id, 1, args[2]);

(Keep in mind that this example may need adjustments based on your specific requirements, but it illustrates the concept of transitioning to async practices)

JavaScript Callbacks and Promises: Exploring Asynchronous Programming

Answer №1

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