Once you run the HTML page again, you will see a check box, Enable coverage, if you check on this, it will populate and display the code coverage information.
I faced two problems while working with blanketjs.
Instead of running from the web server, I tried to execute from normal HTML file, but it was also failing - It was throwing some exception like this - XMLHttpRequest cannot load file:///C:/Demo/scripts/functions.js. Cross origin requests are only supported for HTTP. Looks like blanket.js is trying to load the script function, but it was failing.