Typade resolvers med GraphQL Code Generator

// Without typed resolvers — any type allowed
const userResolver = async (_, { id }) => fetchUser(id);

npm install --save-dev @graphql-codegen/typescript-resolvers

# codegen.yml
generates:
  src/generated/types.ts:
    plugins:
      - typescript
  src/generated/resolvers.ts:
    plugins:
      - typescript-resolvers

import { Resolvers } from "./generated/resolvers";

const resolvers: Resolvers = {
  Query: {
    user: async (_, { id }) => fetchUser(id),
    // Return type enforced: must match User schema
  },
};

interface Context { db: Database; user?: AuthUser; }

// codegen.yml
config:
  contextType: "src/context#Context"

// Generated: Resolvers<Context>
const resolvers: Resolvers<Context> = {
  Query: {
    me: (_, __, ctx) => ctx.user, // ctx: Context
  },
};

# codegen.yml
config:
  mappers:
    User: "src/models#UserModel"

// Typed field resolver on User type
const resolvers: Resolvers<Context> = {
  User: {
    fullName: (parent) => `${parent.firstName} ${parent.lastName}`,
    // parent is UserModel (from mapper)
  },
};

// Schema: createUser(input: CreateUserInput!): User!
const resolvers: Resolvers = {
  Mutation: {
    createUser: (_, { input }) => {
      // input: CreateUserInput — fully typed
      return createUser(input.name, input.email);
    },
  },
};

const resolvers: Resolvers = {
  Subscription: {
    messageAdded: {
      subscribe: () => pubsub.asyncIterator("MESSAGE_ADDED"),
      resolve: (payload) => payload.messageAdded, // typed
    },
  },
};

// package.json
{
  "scripts": {
    "predev": "graphql-codegen",
    "prebuild": "graphql-codegen"
  }
}