What happens first: setTimeout 0 or await Promise.resolve?

so you have 2 async waiting States, but notice that one of them is constant and one is changing (variable). The timeout is set in an XML variable aside while the promise could took forever. If I understood your question quite well, when you have something you rely on take too long and something too short, unless you have a constant applied on one of them like the timeout, then one might end up running shorter unexpectedly (!) Be prepared for that and instead use monolithic structure from code security reasons and not performance.

Promise.resolve will schedule a microtask while setTimeout schedule a macrotask. And the microtasks will run before running the next macrotask.

More information about event loop in general: https://www.youtube.com/watch?v=8aGhZQkoFbQ

More technical details about events loop: https://www.youtube.com/watch?v=cCOL7MC4Pl0