Lasers are a hypothetical, but only if you could basically rake massive areas of space with them, which would require a ridiculous amount of power.
Aren't there laser "weapons" already? I say "weapons" because AFAIK they're only used to shoot down missiles.
That said, yeah, space warfare is pretty hard to imagine. Which is why I just give nearly all sci-fi space battles a pass as long as they look cool. If I was to speculate though, it might involve the conflicting spacecraft to close in on each other like ships-of-the-line of some centuries back.
The USS Ponce is currently deploying a pretty impressive laser system to target fast attack craft. There are no missile defense lasers really - there's some ideas behind blinding and the like, but it's all a bit theoretical.
I don't really believe spacecraft would be closing in on each other in space for a face off. Again, space is REALLY, REALLY BIG - there's absolutely no reason to get even vaguely near something unless you want to. More than that, the laws of physics (as we know them) wouldn't allow you to 'face off' against an opponent in a ships-of-the-line way, the nearest you'd get is hurtling past each other. You could set that up, but with how big space is, I don't see any reason to do so.
More than that, the distances involved would make predicting enemy movement extremely difficult, so anything other than an insanely huge laser rake, or guided drones would be useless.
The only theoretical possibility would be to stop planetary bombardment. However, if that was the case, you'd probably just send the equivalent of hundreds of spaceflight capable drones up to kamikaze anything coming your way.