How to disable Esc button event on alert?

The issue with alert() is that it will always return undefined, giving you no indication of what was pressed. Instead, you can use confirm() which will allow you to display a similar sort of popup.

However, the advantage of confirm is that it returns a true if you clicked "OK" on the popup and false if you pressed esc or "cancel".

Thus, using confirm you can use a do-while loop to keep popping up your popup until the user has pressed "OK" (or pressed the enter key)

See example below:

let res;
do {
  res = confirm("Popup");
} while(!res);

Using the native confirm/alert box isn't a good user experience as it freezes the UI thread. If you can avoid it, I suggest using the DOM to open popups/modals built through HTML. This can easily be done by using a library.