It won't scale in complexity. At a certain point, your mutable state will become really hard to maintain, so you will need some form of state manager. Then your

It won't scale in complexity. At a certain point, your mutable state will become really hard to maintain, so you will need some form of state manager. Then your code will grow and accumulate a lot of bad practices, so you will need a linter. You won't be able to keep the whole codebase in your mind, so you will need more help from your IDE, and you'll end up using Typescript. Your teams will keep overriding each other's CSS, so you will introduce CSS Modules in your build step. The product managers will ask about deeplinking without reloading the page, so you will install a router. Your mutable DOM manipulation code will become full of ifs and special cases, so you will feel the need of abstracting out your components in a declarative way etc. I'm not saying you need all of this from the start, but you will need parts of it pretty soon if your application is heavily interactive.