The typeof type operator

TypeScript adds a typeof operator you can use in a type context to refer to the type of a variable or property:

If we try to use ReturnType on a function name, we see an instructive error:

TypeScript intentionally limits the sorts of expressions you can use typeof on.

// Meant to use = ReturnType<typeof msgbox>
let shouldContinue: typeof msgbox("Are you sure you want to continue?");
',' expected.1005',' expected.