Once you are squarely in a Typescript program and not a "Javascript program gradually adopting Typescript", it would be a good idea to enable Strict mode which forbids implicit-any, effectively meaning the only places you can omit type declarations is where the language will infer the type. Typescript for instance does not infer types of function arguments via their usages (like Flow does), which means in strict mode you must explicitly provide a type for all arguments within a function declaration.

I used to be a bit of a pragmatist when it comes to strict mode, but over the years that has subsided, nowadays I think it is plainly obvious that all Typescript programs should use strict mode unless there's a damn good reason. And I'm not sure there are any legitimate damn good reasons.

True there is no ability to forbid an explicit-any type declaration, though.