With many games it is said that server will assume that clients keep track of the world accurately. Assuming this is true, for a browser based multiplier space invaders game you would only tell the client when new bullets or the players ship moves and everything that behaves in a predetermined manner in the js client.

It would be expected that positions would be the same in the browsers. Do you think you could trust browsers to do this? I feel that timings could differ between rendering loops and cause positions to get out of sync and might just get the server to maintain all the positions to make sure.