Currently, I am faced with the task of implementing client-side validation. Specifically, on a page where a Repeater control is used to generate a list of items. Each item can be selected using a checkbox located in the first column. When the user clicks the 'Delete' button, the selected items are intended to be deleted. To achieve this, I must verify whether the count of selected items is zero or not. My query is: should this type of validation be written in a common .js file or directly on the page itself?