try {
    ...
}
catch (ex) { // Adding an annotation here gives ERROR TS1196: Catch clause variable cannot have a type annotation
    if (ex instanceof FooError) {
        ex; // ex is of type any
        ex.message; // OK
        ex.iDontExist; // typechecks OK, but doesn't exist
    }
    else if (isBarError(ex)) {
        ex; // ex is of type any
        ex.foo(); // typechecks OK, but runtime error
    }
    else {
        ...
    }
}