SvDev, а не проще ли использовать стандартный функционал

Warn on Unsaved Changes

Specify if the user is warned when trying to navigate away from the page, where the page contains unsaved changes. Page Items and Buttons also offer more granular control over when this check is performed, and what is included in it. For Buttons, you can specify if clicking the button will perform the check. For Page Items, you can specify if changes to the item are included, or ignored by the check (see the Warn on Unsaved Changes attribute for both).


в параметрах страницы, раздел Navigation, но правда оно срабатывает, когда в каком то из item были изменения, если не было то дает уйти со страницы