By

user.js

const type = `
  type User {
    id: Int!
    email: String
    courses: [Course]
  }
`

const resolver = {
  courses: () => fetchCourses()
}

course.js

const type = `
  type Course {
    id: Int!
    name: String
  }
`

schema.js

import * as User from './User'
import * as Course from './Course

const schema = `
  ${User.type}
  ${Course.type}
`

const Resolvers = {
  RootQuery: ...
  User.resolver
}