If you use tools like babel to transpile your source code to ES2015 today, you’re already performing something similar to compilation. It’s usually one of the many steps your source code goes through before reaching the end-user. If you’re not, then moving to a compiled language is a valid concern. To put your concerns at ease. Reason is very fast. I use a lot of tooling to create modern React applications including webpack, babel and flow. It can take a minute from a cold start and a few seconds whenever a change is made. It didn’t seem like that long but then I used Reason which builds in milliseconds. I wish all compiled languages were this fast, I’m amazed by the performance and it hasn’t posed a problem yet.