How to remove standard message when a document is about to unloaded?

The onbeforeunload event occurs when a document is about to be unloaded.

This event allows you to display a message in a confirmation dialog box to inform the user whether he/she wants to stay or leave the current page.

The default message that appears in the confirmation box, is different in different browsers. However, the standard message is something like “Are you sure you want to leave this page?”. There are two buttons Leave and Cancel.

This message can be removed, by call preventDefault() on the event.

function fieldChanged(scriptContext) {
        window.onbeforeunload = function(event) {
            event.preventDefault()
        };

    }