Some languages allow to define type alias, name of this type can be self-explanatory:

  type FullName = string;
  function combineName(first: string, last: string): FullName;

Also documentation comment for function is what specifically solves this - describes what function does and returns.

Neither really addresses the issue. Making a type for a single kind of string seems like an abuse of types just to shoehorn the documentation in. Documentation can be used directly of course, but that moots all of this -- just document? Yeah, but naming the variable is super quick compared to either.

Variable names is just documentation. Having types that can assert some condition on the underlying value is not even comparable to "having a named return variable". (just document? just name variables?) You don't care about what the name of the returned value is, you care about what *it is*.

Typescript nukes primitive aliases like this sadly. Intellisense will just infer it as "string".

you can do this rather easily by returning an object rather than a primitive. if you're using a language like TypeScript, destructuring the resulting returned object is rather trivial and (in my opinion) delightful to read. eg

  function combineNames({ first, last }) {
    const fullName = `${first} ${last}`;
    return { fullName };
  }
  const { fullName } = combineNames({first: 'John', last: 'Doe' });

For some reason React prefers to return arrays. I never understood the reason.

  const [state, setState] = useState(initialState)

instead of

  const {state, setState} = useState(initialState)

I fail to see the distinction, for documentation purposes, of this versus just giving it that `getFullName` function name.

A more complex example will probably return a more complex type that is more self-documenting. If the type is a single scalar value then I don't see the value of adding another name here.

Similarly to passing an object argument, you can return an object.

Then pair it with destructuring assignment!

`const { fullName } = getName({ firstName, lastName )}`

Name the function/method as the thing it "returns".

In fact, just forget that it is a function that does something. Treat it as the thing it returns.

string fullName( string firstName, string lastName )