It would be more accessible to have a confirmation page within the CMS itself, not using javascript, because users who have javascript disabled, or use screen-reader based browsers (that is, browsers for visually-impaired people) would probably run into problems, and might end up deleting pages without meaning to.
The confirmation page would be pretty simple to incorporate into your CMS - something like:
PHP Code:
if(isset($_GET['confirm'])){
if($_GET['confirm']==true){
// Page deletion code here.
}
} else {
echo "Are you sure you want to delete this page? This action can not be undone.<br />";
echo "<a href=\"index.php?act=delete&id={$_GET['id']}&confirm=true\">I'm sure.</a> "; // {$_GET['id']} inserts the page to delete from the URL of the page you're currently on
echo "<a href=\"\">Cancel.</a>"; // Point this link to previous page
}