Returns the "keys" or the "values" of an object.
keys { a: 'A', b: 'B' }
# f.ret --> [ 'a', 'b' ]
values { a: 'A', b: 'B' }
# f.ret --> [ 'A', 'B' ]
When used against an array, the indexes will be the numerical indexes 0 to array length - 1.
keys [ 1, 'to', true ]
# f.ret -> [ 0, 1, 2 ]
values [ 1, 'to', true ]
# f.ret -> [ 1, 'to', true ]
When used against something that is neither an object nor an array it will fail.