graphql-typed-client/src/schema/fetchSchema.ts

A tool that generates a strongly typed client library for any GraphQL endpoint. The client allows writing GraphQL queries as plain JS objects (with type safety, awesome code completion experience, custom scalar type mapping, type guards and more)

import 'isomorphic-fetch'
import { buildClientSchema, ExecutionResult, getIntrospectionQuery, IntrospectionQuery } from 'graphql'
import { GraphQLSchemaValidationOptions } from 'graphql/type/schema'
import qs from 'qs'

export interface SchemaFetcher {
  (query: string, fetchImpl: typeof fetch, qsImpl: typeof qs): Promise<ExecutionResult<IntrospectionQuery>>
}

export const get = <T>(uri: string, query: { [arg: string]: any }): Promise<T> =>
  fetch(`${uri}?${qs.stringify(query)}`).then(r => r.json())

export const post = <T>(uri: string, body: { [arg: string]: any }): Promise<T> =>
  fetch(uri, {
    method: 'POST',
    body: JSON.stringify(body),
    headers: { 'Content-Type': 'application/json' },
  }).then(r => r.json())

export const fetchSchema = async (endpoint: string, usePost = false, options?: GraphQLSchemaValidationOptions) => {
  const result = usePost
    ? await post<ExecutionResult<IntrospectionQuery>>(endpoint, { query: getIntrospectionQuery() })
    : await get<ExecutionResult<IntrospectionQuery>>(endpoint, { query: getIntrospectionQuery() })

  if (!result.data) {
    throw new Error('introspection request did not receive a valid response')
  }

  return buildClientSchema(result.data, options)
}

export const customFetchSchema = async (fetcher: SchemaFetcher, options?: GraphQLSchemaValidationOptions) => {
  const result = await fetcher(getIntrospectionQuery(), fetch, qs)

  if (!result.data) {
    throw new Error('introspection request did not receive a valid response')
  }

  return buildClientSchema(result.data, options)
}