Several ES6 additions are only available in strict mode. Example:
> SyntaxError: Block-scoped declarations (let, const, function, class) not yet supported outside strict mode
Strict mode was also enabled in a few of our files already, and it is a good thing to have anyway.
Currently, for join/part/kick/nick/... the server will send an updated list of users and the client will re-render the list entirely. This ends up being a very expensive operation when joined on large channels and causes the client to slow down a lot.
