Exceptions during AJAX requests in JavaScript

If an exception occurs while executing an AJAX request (for example, the Internet is interrupted), then the promise will end with an error. We can catch this error in a convenient way, for example, through catch:

button.addEventListener('click', function() { let promise = fetch('/ajax.html') .then( response => { return response.text(); }, ).then( text => { console.log(text); } ).catch( error => { alert(error); } ); });

Output a text of a page if the request was successful, and an error if there was a network error.