Printing certificates without an LMS

I'm try to get my SL2 created course to print the certificate that comes up when a user completes all of the lessons.  I tried this idea - 

Brett Rockwood

I too know next to nothing about javascript but I believe if you add the following as a your script it will print the current window:

window.print();

At least is worked for me once...

Although it brings up the printer settings it only prints the copyright notice at the bottom of the page. I tried it in both Chrome and Firefox.  Do I need to put something between the parentheses?  I know very little about Javascript in SL2 and would be thrilled to have a class on it at DevLearn.