stockfish.js | strong open source chess engine Stockfish | Binary Executable Format library

The await keyword, didn't have any effect in your code because the function stockfish.postMessage doesn't return a Promise. postMessage emits an event that will be processed in the next tick. This is why console.log('test3') was logged after console.log('test2'). After emitting the event it will return synchronously, logging console.log('test2').

stockfish.onmessage will need to be the control centre of all events. It will need to understand the different messages, and do the appropiate actions. You dont need to put the implemention of the actions in the onmessage. You can create a function and called it from stockfish.onmessage... and then inside the action function you could call to stockfish.postMessage if you need to notify stockfis of a change... and so on.... and on...