Set a limit on a registration form

[appoidapittee]

I have an asp classic Event registration jquery form. what I would like to do is display a number spaces available on my registration page like "Available Space: 20" after user filled up the form they will get an email and also we have an XML file which the info is stored there.Is there a way to read the XML file with JS,JQ or ASP and show how many available written on a xml?