graphql-interace.js

const typedef = `
interface Character {
  name: String
}

type Human implements Character {
  name: String
}

type Robot implements Character {
  name: String
  engine: String
}

type Query {
  allCharacters: [Character]
}
`

const resolvers = {
  Character: {
    __resolveType(character) {
      if (character.engine) {
        return 'Robot'
      }
      return 'Human'
    }
  },
  Query: {
    allCharacters() {
      return [{ name: 'P1' }, { name: 'P2' }, { name: 'Robot1', engine: 'Fuel' }]
    }
  }
}