[navaati]

EDIT: see paavohtl's comment: I hadn't payed attention to the types, dumb me.

You're right, because for a pair of functions f and g, you have an isomorphism if:

  f(g(x)) == x

  g(f(x)) == x

for every x. However, here of course

  (([a]) => {a})( (({ a }) => [a])({ key: 'data'}) )

is equal to

  { a: 'data' }

The OP doesn't quite master what he's talking about…