Using Javascript to truncate the filename?

I want to display the URL in a Model View Controller fashion, using ordinary Javascript.

But, not using MVC. And with a unique ID.

For example,
mydomain.com/play/F01235

So, I would have a play.html and play.js

which reads the input param, loads the page and responds to a click event when the user clicks on the page.

How do I do this with ordinary Javascript?

Thanks