This is why TypeScript is so popular. JavaScript is very loose, but you can progressively enhance it using TypeScript with stricter and stricter types, many of which can be inferred, and since 3.7 can be derived by runtime assertions, and the strictness of which can be controlled with compiler flags.

Additionally, it is fairly typical in js to use functional programming styles, making type inference a breeze / provable / not introducing much boilerplate by adding types.