The unknown type instead of any

The any type switches off the compiler's checks: every operation on it is allowed, and every mistake slips through to runtime. JSON.parse returns any, so data from the outside world enters your code unchecked. Run the starter code and look at 30001: the port number arrived as a string, so the addition turned into string concatenation.

unknown is the opposite. It accepts any value, but it won't allow any operation on it until you've confirmed its type. You use typeof, !== null and in to narrow the type step by step until the value is safe to use.

Watch out for a common mistake: typeof null === "object", so checking typeof data === "object" on its own isn't enough before you read a property from the value.