The Frost Guard in Brendon's post is the same one I use on my daughter's CR-V. It's an almost-perfect fit on that vehicle, but would provide incomplete coverage on the JL. FWIW, those guards/covers do work.
When I had my YJ during a cold/wet/snowy Pennsylvania winter, I scientifically cut a large piece of cardboard to match the profile of the windshield on that vehicle. It worked quite well as a frost guard, but for its abbreviated service life.
Using the original as a template, I kept several spares on hand and deployed them only when the overnight forecast was particularly nasty. Otherwise, I'd use a scraper. That rig had a good defroster. More to the point, the windshield was the only glass on that vehicle, so getting ready each morning didn't take very long.
Alternatively, a deicer spray also works quickly and well. Buy several cans, as they tend to empty quickly even when the user is being frugal with the spray.