[fenomas]

I made an ECS in JS and have been using it for some time. It's not particularly designed for the kind of rollback you're talking about, but you might find it useful as a comparison:

https://github.com/andyhall/ent-comp

In mine I store each entity's state for a given component as an object (e.g. `{ mass:1, velocity:[0,0,0] }`, so the internal storage of the ECS for a given component is an array of such objects. To really optimize for the "cache and rollback" kind of behavior you're talking about I guess it would be ideal for the internal storage to be flat arrays of numbers, but at first blush it seems like that would make the implementation of the ECS itself kind of hairy.