How to type return value as "throw"

Question

Sometimes my function will throw. I want to add this to the return type. In TypeScript we set the return type to never. Is there an equivalent strategy in Flow?

Answer 1

Flow have empty type. Take a look at example of Typing Redux reducers, also can work as returned type for function.

/* @flow */

function foo():empty {
    throw new Error();
}

function baz():empty {
    return 42;
}

    return 42;
           ^ Cannot return `42` because number [1] is incompatible with empty [2].
References:
8:  return 42;
           ^ [1]
7: function baz():empty {
                  ^ [2]