What is the chemical reaction NH3 H2O NH4 OH?

There are two types of bonding in NH4OH: covalent and ionic. That is because it is composed of two complex ions, NH4+ and OH-. That bond that holds these two complex ions together is ionic, but the bonds that exist between the atoms of the complex ions themselves is covalent.
In other Words, the bonds between the nitrogen (N) and the 4 hydrogens (H) is covalent, and so is the bond between oxygen (O) and hydrogen. However the bond between NH4+ and OH- is ionic.