Can websocket messages arrive out-of-order?

Question

If we send two messages over the same html5 websocket a split millisecond apart from each other,

Is it theoretically possible for the messages to arrive in a differ

Answer 1

Short answer: No.

Long answer:

WebSocket runs over TCP, so on that level @EJP 's answer applies. WebSocket can be "intercepted" by intermediaries (like WS proxies): those are allowed to reorder WebSocket control frames (i.e. WS pings/pongs), but not message frames when no WebSocket extension is in place. If there is a neogiated extension in place that in principle allows reordering, then an intermediary may only do so if it understands the extension and the reordering rules that apply.