Is NH4OH a covalent or ionic compound?

As written, it is an ionic compound.
As written this is ammonium hydroxide, and it is comprised of two ions: ##[“NH”_4^+][“OH”^-]##.
As noted in the comments, ammonium hydroxide actually is a solution of ammonia and water in equilibrium, with the ammonia and water mixture being more favorable.
##”NH”_3 + “H”_2″O” rightleftharpoons “NH”_4^+ + “OH”^-##
Considering the context of the initial question, I would classify the compound as written as ionic.