To show the "Are you sure you want to navigate away from this page?" message when changes committed with JavaScript, we set the window.onbeforeunload property to a function that returns a truthy value.
For instance, we write
window.onbeforeunload = () => {
return true;
};
to set window.onbeforeunload to a function that returns true to show the "Are you sure you want to navigate away from this page?" message before the tab or window is closed or navigation starts.
