Do you realize that the Typescript example contains strictly more information than the Javascript one (namely, declarations for the type of three things) and is therefore more complex to compile, while the two C++ examples are semantically identical (the last expression in the function is returned implicitly without having to write "return") and the new syntax is easier to parse?

There are several semantic differences between Cpp1 and Cpp2. Cpp2 moves from last use, which is the biggest one. In a contrived example, that could result in a "hello world" changing to "goodbye world" or any other arbitrary behavior change you want to demonstrate. Cpp2 also doesn't require you to order functions and types or declare prototypes, which means partial template specializations and function overloads can produce similar changes when migrating from Cpp1 to Cpp2.