To run apollo client against a local schema

apollo-local-link.ts

import { ApolloLink, Observable } from 'apollo-link'

import { execute, GraphQLSchema } from 'graphql'

export class LocalLink extends ApolloLink {
  schema: GraphQLSchema

  constructor(schema: GraphQLSchema) {
    super()

    this.schema = schema
  }

  request(operation: any): Observable<any> {
    const { schema } = this
    const { query, variables, operationName } = operation

    return new Observable((observer) => {
      let canceled = false

      // We get a MaybePromise from the execute function
      Promise.resolve(execute(schema, query, null, null, variables, operationName))
        .then((result) => {
          if (canceled) {
            return null
          }
          // we have data and can send it to back up the link chain
          observer.next(result)
          observer.complete()

          return result
        })
        .catch((err) => {
          if (canceled) {
            return
          }

          observer.error(err)
        })

      return () => {
          canceled = true
        }
    })
  }
}