Node JS callbacks in a while loop - mysql

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

Answer 1

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());