Attack speed in Diablo 4 is an offensive stat.
An Attack Speed bonus is capped at 100%. However, this can be exceeded with gear and abilities. Essentially there are two damage buckets in play for Attack Speed.
Calculation
To work out the total Attack Speed the following calculation[1] can be carried out.
Total Attack Speed = min(sum of all Attack Speed which cannot exceed the cap,100%) + sum of all Attack Speed which can exceed the cap
Attack Speed also affects the time it takes for a skill to activate. Research also suggests that Attack speed is more benefifial on faster weapons.