if wasd control schem, ususally the jkl keys are used for jumping, attacking and stuff.
if it's arrow key movement games usually use
xcz (which is a royal pain for german casuals since with german keyboards, the bottom row of keys is yxc (namely its a qwertz keyboard), so you have to have an weird way of moving your left hand)
anyways xcz is in this case used for attack, jump and stuff.
but this is jsut my basic observation how simple browser games commonly place their controls. if it needs more than 3 basic actions, then stuff gets more complicated anyways.
but yeah, for browser games (or actually any sort of game) I prefer pure keyboard too.
cause if one hand has to be on the mouse, then the other hand can literally only be used for movement and nothing else :-)