Node JS callbacks in a while loop

Question

I have a MySQL database with the table id which stores all the unique id's generated till date, using nanoid module. I have implemented the following code to generate a unique id which is not in the table.

//sql library
const mysql = require('mysql');
const sql_obj = require(__dirname + '/../secret/mysql.json');


//nanoid library
const { customAlphabet } = require('nanoid');
const alphabet = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789';
const nanoid = customAlphabet(alphabet, 30);

function uniqueid(){
    let found = 0;
    let conn = mysql.createConnection(sql_obj);
    while (found === 0){
        let id = nanoid();
        conn.connect(function(err){
            if (err){
                found = 2;
            }
            else{
                conn.query("SELECT * FROM id WHERE value = " + mysql.escape(id),function(err,result,fields){
                    if (err){
                        found = 2;
                    }
                    else{
                        if (result.length === 0){
                            found = 1;
                        }
                    }
                })
            }
        })
    }
    if (found === 2){
        return {error: 1,ret: null};
    }
    else if (found === 1){
        return {error: 0,ret: id};
    }
}

console.log(uniqueid());

I knew, my implementation is wrong. Because callbacks are asynchronous in nature, the while loop never ends and hence I got the error JavaScript heap out of memory.
I went through many articles in the web to sort this out, but couldn't. The main problem is that the function uniqueid should return some value, because, I am calling it from other JavaScript file.
Thanks for any help

Murat Colyaran · Accepted Answer · 2021-05-08 19:00:23Z

I think best way to prevent this is using async/await.

I promisified your mySql connection. And you can send your query and values to the function.

    //sql library
    const mysql = require('mysql');
    const sql_obj = require(__dirname + '/../secret/mysql.json');


    //nanoid library
    const { customAlphabet } = require('nanoid');
    const alphabet = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789';
    const nanoid = customAlphabet(alphabet, 30);

    let db = (query, values = null) => {  
        return new Promise((resolve, reject) => {
            let conn = mysql.createConnection(sql_obj);
            conn.connect(function (err) {
                if (err) {
                    reject(err);
                }
                else {
                    conn.query(query + values, function (err, result, fields) {
                        if (err) {
                            reject(err);
                            return;
                        }
                        else {
                            if (result.length === 0) {
                                resolve();
                            }
                        }
                    })
                }
            })
        })
    }

    async function uniqueid() {
        while (found === 0) {
            let id = nanoid();
            try {
                await db("SELECT * FROM id WHERE value =", mysql.escape(id));
                return { error: 0, ret: id };

            } catch (error) {
                return { error: 1, ret: null };
            }
        }
    }

    console.log(uniqueid());

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