Javascript has a lot of reserved words that are not actually used by the language which I think were reserved for possible future use. class is one of these even though Javascript does not actually use classes. Another is goto and there's absolutely no chance of that ever being used. The result, however, is that if you want to use these as a json key then it has to be quoted. Strictly speaking you should probably always quote your keys just to avoid the possibility of falling foul of the javascript unused reserved word trap (mind you - I never do).
