Even i used to think the same way but soon realized that its not possible to stay without js. Take for example you want to show a alert message or get a confirmation from the user on the client side. You might think that using MessageBox.Show() would do the trick but it fails on many occasion as its a windows class library function. Instead you have to write something like this. in the head section of your html document inside the scripts tab("script").
var ans= confirm("Are you sure you want to do this?")
Well this is a good example for very first starters and you might find many other stuff accross the internet.