AJAX Call Via Vanilla JavaScript In WordPress Plugin Development

I ama newbie in WordPress Plugin development in which I have some HTML form on the main plugin page that will get the data from the admin who is logged in and a back page where I have some different functions in PHP like to get information from the database etc. To explain in detail, here is the code…

Add a preview to a WordPress Control Panel

I’m trying to create a new wordpress template and inside it I added a Control Panel, inside this control panel there is an option that allows user to choose where he want’s to place a on a map, I try to explain: user can set div’s left and top attributes via control panel.
Now I know how to add an iframe that can show a preview of the changes but it doesn’t work as I would like (how to add the preview? read here: Modify CSS via Theme Control Panel) What I would like to add is a real time preview. As soon as the user modify TOP or LEFT attribute preview has to show what it is happening without showing it to “live” blog.