Error from node-js mysql connection doesn't get saved to array

Question

Im trying to keep a record from all my errors in a WebService I'm making in node-js;

I've written the following code to keep track of a mysql query possible error:

        var err_db = [];

    try{
        if(error.length == 0){
            ...
            var con = mysql.createConnection({
              host: "my_host",
              user: "my_user",
              password: "my_pass",
              database: "my_db"
            });

            con.connect(function(err) {
              if (err) err_db[err_db.length] = err.message;
              con.query("IM TRYING HARD TO GET AN SQL ERROR", function (err) {
                if (err) err_db[err_db.length] = err.message;
                console.log(err_db); //FIRST LOG SHOWS CORRECT
              });
              console.log(err_db); // THE ERROR DISAPEARS FROM ARRAY
            });
        }
    }
    catch(err){
        if(err) err_db[err_db.length] = err.message;
    }

The problem is the error only keeps stored in array inside the con.query function, after that it disappear, and I want to keep it in a array because later on I intend in sending this possible errors as a JSON to through the WebService response. Thanks in advance.

Ankit · Accepted Answer · 2018-09-10 05:54:43Z

2

This is a normal asynchronous nature of node.js. Since the query is executed in a slight greater time so next line is executed first.

try{
        if(error.length == 0){
            ...
            var con = mysql.createConnection({
              host: "my_host",
              user: "my_user",
              password: "my_pass",
              database: "my_db"
            });

            con.connect(function(err) {
              if (err) err_db[err_db.length] = err.message;
              con.query("IM TRYING HARD TO GET AN SQL ERROR", function (err) {
                if (err) err_db[err_db.length] = err.message;
                console.log(err_db); //FIRST LOG SHOWS CORRECT
               // throw the error from here 
              });
              console.log(err_db); // THIS EXECUTED EARLIER THAN THE PREVIOUS
            });
        }
    }
    catch(err){
        if(err) err_db[err_db.length] = err.message;
    }

answered Sep 10, 2018 at 5:54

Ankit

9906 silver badges12 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Eduardo Amaral Over a year ago

Thanks a lot for the help!

LPZ · Accepted Answer · 2018-09-10 03:56:03Z

1

Asynchronous code cannot catch exceptions using try-catch.

You can try the following code.

var EventEmitter = require('events');
var emitter = new EventEmitter();
var err_db = [];

var con = mysql.createConnection({
  host: "my_host",
  user: "my_user",
  password: "my_pass",
  database: "my_db"
});

if (error.length == 0) {
  con.connect(function (err) {
    if (err) {
      emitter.emit('err_db', err);
      return;
    }
    con.query("IM TRYING HARD TO GET AN SQL ERROR", function (err) {
      // if (err) err_db[err_db.length] = err.message;
      // console.log(err_db); //FIRST LOG SHOWS CORRECT
      if (err) {
        emitter.emit('err_db', err);
        return;
      }
    });
    console.log(err_db); // THE ERROR DISAPEARS FROM ARRAY
  });
}

emitter.on('err_db', (err) => {
  // handle db err...
  err_db[err_db.length] = err.message
});

answered Sep 10, 2018 at 3:56

LPZ

693 bronze badges

1 Comment

Eduardo Amaral Over a year ago

Thanks a lot! Didn't realize this was an asynchronous function.

Collectives™ on Stack Overflow

Error from node-js mysql connection doesn't get saved to array

2 Answers 2

1 Comment

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

1 Comment

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related