You don't need to. One if statement to check that is not a problem. The problem occurs when you have a bunch of other ifs as well to check all kinds of other stuff that a type system would handle for you like nullability, incorrect types etc.

Personally I just write JS like a typed language. I follow all the same rules as I would in Java or C# or whatever. It's not a perfect solution and I still don't like JS but it works.