PROBLEM:

I tried to follow your tutorial but I get an error. In fronted I  read "Undefined" instead of the check-box.

SOLUTION:

Upgrade to version 1.8.3 or above.

DISCUSSION:

The problem arose from an incorrectly phrased "case" in a "switch" statement which failed to check for when you want to use CSS and have the label appear after the button/box.