vanderwaal's force is merely a force of attraction b/w two molecules. It occurs when the protons of one molecule attract the electrons of the other.
Ionic bond however is the bond formed by sharing of an electron b/w a metal and a non metal.
Strength of a vanderwaal's force of attraction depends on the molar mass of the molecule as more the number of protons and electrons more will be the force of attraction.
Strength of an ionic bond depends on the difference in electro negativity of the two atoms participating in bond formation.