Yes you can and it has been done with a bit of success. Fordana - a multiplayer RPG - would probably be the most popular javascript game, although it has been shutdown for a while. I played it during public beta and as you probably know, it's ridiculously easy to hack. Anyway, you could make a game in Javascript, but it would most likely be in vain for the above mentioned reasons.you can't write a game in javascript.
JS games don't have to be static and Fordana was not.Bleh, Javascript is not intended for making games, you can't use 3d libraries etc. So basically you would get a game with static images and/or text which sucks real much. And Flash is extremely gay, ugly as hell and not intended for mmorpg's either. So, nothing beats machine languages (and bytecode languages) when writing games.
Why would you want to make a game like runescape?

