Typescript has a config option (allowJs: true) that does exactly this -- types where you want them, regular ES6 when you don't. I type things like component Pro

Typescript has a config option (allowJs: true) that does exactly this -- types where you want them, regular ES6 when you don't. I type things like component Props/State, reducers, global state, and domain models. For everything else I tend to use regular, idiomatic JS.