I use nodejs and mysql for my app. I do the DB query in such manner:

try {
    myDB.query(SQL, object, (err, res) => {
        if (err) throw err
        ...
    }
} catch (err) {
    console.log(err.message)
}

But this is do not work because of async query func. So how to catch those errors, which is can occur in callback? Please help.

I use nodejs and mysql for my app. I do the DB query in such manner:

try {
    myDB.query(SQL, object, (err, res) => {
        if (err) throw err
        ...
    }
} catch (err) {
    console.log(err.message)
}

But this is do not work because of async query func. So how to catch those errors, which is can occur in callback? Please help.

• javascript
• mysql
• node.js

2 Answers 2

You can't throw inside of async code with callbacks. You must use async error handling:

function makeQuery(callback) {
  myDB.query(SQL, object, (err, res) => {
    if (err) {
      callback(err)

      return
    }

    ...
  }
}

It's up to the caller to provide a suitable callback function that takes (err, response) or something similar. It's also the responsibility of the caller to intercept, handle, or forward any and all errors.

If you use Promise-driven code you can either use .catch() or async functions with await that will work inside try. Sequelize is a good Promise-driven database driver.

Then you have code that looks like this:

let result = await myDB.query(SQL, object)

Which is obviously a lot cleaner.

You could use this example:

try {
  connection.query('SELECT * FROM ??',[Table], function (err) {
    if (err) console.error('err from callback: ' + err.stack);
  });
} catch (e) {
  console.error('err thrown: ' + err.stack);
}

for example. if "Table" does not exist, you would have the response:

'Table' doesn't exist

EDIT:

what @tadman says is correct, if you use if (err) throw err, you are only generating an exception error and you lose what you need.