Catching exception errors when logging in via NodeJS + MySQL - mysql

Question

Recently I've been trying to learn NodeJS to set up a log in process, so I decided to write all the errors and make exceptions for them. My question is how can I make sure each if is responsible for each error code. I haven't worked with try and catch before so this is a new territory for me.
Also is it better to use multiple try-catch or should I consider using 1 block where I can use a switch for example (used else if here as a quick example).
Table with Status errors
0 - no connection with database.
1 - connection ok but we dont have any privileges for access to the
database or something like that.
2 - all ok.
3 - ok, but no data found in query results.
4 - error getting results of query.
5 - other.
module.exports = (username,password,connection ) => {
var data ={
"Status" : null,
"Data" : {} //JSON results inside of Data Json
}
try{
connection.query("SELECT id FROM players", function (error, results, fields) {
if (error){
data.Status = 0;
data.Data= "No connection can be established with the database";
return data
}
else if(error){
data.Status = 1;
data.Data= results + "Connection OK but no priviliges";
return data
}
else if(error){
data.Status = 2;
data.Data=results + "connection running";
return data
}
else if(error){
data.Status = 3;
data.Data=results + "No data found in query results";
return data
}
else if(error){
data.Status = 4;
data.Data=results;
return data
}
else if(error){
data.Status = 5;
data.Data=results;
return data
}
});
}
catch(e){
console.log(e);
data.Status= 2;
data.Data=null;
return data;
}
};

Answer 1

Welcome to async programming, your try/catch block won't do anything for any I/O process, all errors are handled by error object in the callback function. (unless you use the last async/await ES6 pattern)
connection.query("SELECT id FROM players", function (error, results, fields) {
if (!error) { // no error, return results
data.status = 2;
data.Data = results;
return data;
}
// for all error code, please check mysql library document
// https://www.npmjs.com/package/mysql#error-handling
if (error.code === 'ER_ACCESS_DENIED_ERROR') {
data.Status = 1;
data.Data=results;
return data
}
// handle any other error codes
// if ....
});
Edit: please note that, your exported function in module.exports won't return anything because you are calling database query which is an async I/O process and requires another callback function to get the data returned by database

Answer 2

This will never work as expected :
if (error){
console.log("I'm the error");
return;
} else if(error){
console.log("I will never be display on error because of return in the first if");
}
Should be :
if (!error){
// No error
} else if(error === 'something'){
// Error something
} else if ....
// Other type of error
} else {
// Unknown error
}
You can use a switch instead in a more elegant way :
const data = { Status: 1, Data: results }
if(error) {
switch(error.code) {
case 'ER_ACCESS_DENIED_ERROR' :
data.Satus = 2;
return data;
...
}
}
return data;