JQuery Custom Validation Rule Mysql function always showing error

I am trying to add a custom validation rule to check if username exists or not. My code:

jQuery.validator.addMethod("checkexist", function(myvalue, element) {
    checkifexist(function(result) {
      if (result == true)
      {  
            return true;
      }
      else
      {
          return false;
      }
    });
}, 'Does not exists!');

and

async function checkifexist(callback) {
const secret = keytar.getPassword('Userdata', 'MysqlPassword');
secret.then((result) => {
  var mysql = require("mysql");
  var connection = mysql.createConnection({
  host: store.get('ip'),
  port: store.get('port'),
  user: store.get('username'),
  password: result,
  database: "database"
});     
  
var querystring = 'SELECT * FROM `testdb`';
try
{
  connection.query(querystring, (err, rows, fields) => {

    if(err){
      return callback("error with query", err);
    }

    var found;
    for (var i in rows)
    {  
        if (some check...)
        {
        return callback(true);
        }          
    }

    return callback(false);
    
});
connection.end(() => {
});
}
catch { }

});

However, if I check the valditation it correctly outputs true or false on every keypress. I still get only validation errors, though it should be a valid input.