>If you write sync code and later you need it to be async, then you're in for a full rewrite
If you just want it not to block using the page then you can just chain the sync code into a bunch of async callbacks. For actually parallelizing tasks that weren't before, it can be harder, but in my experience still not a full rewrite. It is much harder for larger applications in other contexts like the migration of Firefox to Quantum, though, yes.
If you just want it not to block using the page then you can just chain the sync code into a bunch of async callbacks. For actually parallelizing tasks that weren't before, it can be harder, but in my experience still not a full rewrite. It is much harder for larger applications in other contexts like the migration of Firefox to Quantum, though, yes.