# Exceptions in asynchronous callbacks in JavaScript

Let, if the number of a non-existent array element is passed as the `make` parameter, then this is an exceptional situation. As you already know, exceptions thrown inside an async function cannot be caught with `try-catch`. In our case, an exception thrown inside `make` or a callback will not be caught:

`try { make(10, function(res) { console.log(res); }); } catch(err) { // it won't get caught }`

In the callback approach, they work as follows with exceptions: the result is sent to the first callback parameter, and the error is sent to the second. In this case, the error handling is as follows:

`make(10, function(res, err) { if (!err) { console.log(res); // no error occurred, we output the result } else { console.log(err); // an error has occurred, we output its text } });`

Let's rewrite our `make` function code as described:

`function make(num, callback) { setTimeout(function() { let arr = [1, 2, 3, 4, 5]; let err; if (arr[num] === undefined) { err = 'elem not exists'; // an error text } else { err = null; // no error } callback(arr[num], err); }, 3000); }`
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