The documentation clearly states that functions edgeLength and hexArea allow for second parameter to be UNIT.rads for edgeLength or UNIT.rads2 for hexArea. However when calling these functions:
h3.edgeLength(12, h3.UNIT.rads);
h3.hexArea(12, h3.UNIT.rads2)
an error is thrown:
Unknown unit: rads
Unknown unit: rads2