Is it save to rely on the order of messages passed from the main thread to a single Web Worker being retained? For instance, if I do
worker.postMessage(1);
worker.postMessage(2);
will the worker certainly get to process the first message before the second one?
As long as you are working with the same worker to post the messages, I think it will. You can easily test this if you want. Make a loop and post messages with a certain order. If you always receive the messages in the same order as you post them, you can relay on it, that this will be the case.