Can you make a graphql type both an input and output type?

While working on a project I had a similar problem with code duplication between input and type objects. I did not find the extend keyword very helpful as it only extended the fields of that specific type. So the fields in type objects cannot not be inherited in input objects.

In the end I found this pattern using literal expressions helpful:

const UserType = `
    name: String!,
    surname: String!
`;

const schema = graphql.buildSchema(`
    type User {
        ${UserType}
    }
    input InputUser {
        ${UserType}
    }
`) 

You can do something like this:

export const createTypes = ({name, fields}) => {
  return {
    inputType: new InputObjectType({name: `${name}InputType`, fields}),
    objectType: new ObjectType({name: `${name}ObjectType`, fields})
  };
};

const reservation = createTypes({
  name: "Reservation",
  fields: () => ({
    hotelId: { type: IntType },
    rooms: { type: new List(RoomType) },
    totalCost: { type: new NonNull(CurrencyType) },
    status: { type: new NonNull(ReservationStatusType) }
  })
});
// now you can use:
//  reservation.inputType
//  reservation.objectType

In the GraphQL spec, objects and input objects are distinct things. Quoting the spec for input objects:

Fields can define arguments that the client passes up with the query, to configure their behavior. These inputs can be Strings or Enums, but they sometimes need to be more complex than this.

The Object type... is inappropriate for re‐use here, because Objects can contain fields that express circular references or references to interfaces and unions, neither of which is appropriate for use as an input argument. For this reason, input objects have a separate type in the system.

An Input Object defines a set of input fields; the input fields are either scalars, enums, or other input objects. This allows arguments to accept arbitrarily complex structs.

While an implementation might provide convenience code to create an object and a corresponding input object from a single definition, under the covers, the spec indicates that they'll have to be separate things (with separate names, such as Reservation and ReservationInput).

this is something that i did for my project (works good):

const RelativeTemplate = name => {
  return {
    name: name,
    fields: () => ({
      name: { type: GraphQLString },
      reference: { type: GraphQLString }
    })
  };
};
const RelativeType = {
  input: new GraphQLInputObjectType(RelativeTemplate("RelativeInput")),
  output: new GraphQLObjectType(RelativeTemplate("RelativeOutput"))
};