vladshcherbin / graphql-api-koa

GraphQL execution and error handling middleware written from scratch for Koa.

graphql-api-koa

GraphQL execution and error handling middleware written from scratch for Koa.

Setup

To install graphql-api-koa and the graphql peer dependency with npm, run:

npm install graphql-api-koa graphql

See the execute middleware examples to get started.

API

Table of contents

• function errorHandler
• function execute
• type ErrorGraphQLResolver
• type ErrorKoaMiddleware
• type ExecuteOptions
• type ExecuteOptionsOverride

function errorHandler

Creates Koa middleware to handle errors. Use this before other middleware to catch all errors for a correctly formatted GraphQL response.

Special Koa middleware error properties can be used to determine how the error appears in the response payload errors array and the response HTTP status code.

Special GraphQL resolver error properties can be used to determine how the error appears in the response payload errors array.

Additional custom Koa middleware can be used to customize the response.

Returns: Function — Koa middleware.

Examples

Ways to import.

import { errorHandler } from 'graphql-api-koa';

import errorHandler from 'graphql-api-koa/public/errorHandler.mjs';

---

function execute

Creates Koa middleware to execute GraphQL. Use after the errorHandler and body parser middleware.

Parameter	Type	Description
options	ExecuteOptions	Options.

Returns: Function — Koa middleware.

Examples

Ways to import.

import { execute } from 'graphql-api-koa';

import execute from 'graphql-api-koa/public/execute.mjs';

A basic GraphQL API.

import Koa from 'koa';
import bodyParser from 'koa-bodyparser';
import { errorHandler, execute } from 'graphql-api-koa';
import schema from './schema.mjs';

const app = new Koa()
  .use(errorHandler())
  .use(
    bodyParser({
      extendTypes: {
        json: 'application/graphql+json',
      },
    })
  )
  .use(execute({ schema }));

---

type ErrorGraphQLResolver

A GraphQL resolver error may have these special properties for the errorHandler Koa middleware to use to determine how the error appears in the response payload errors array.

Type: object

Property	Type	Description
message	string	Error message. If the error expose property isn’t true, the message is replaced with Internal Server Error in the response payload errors array.
extensions	object<string, *>?	A map of custom error data that is exposed to the client in the response payload errors array, regardless of the error expose or status properties.
expose	boolean?	Should the original error message be exposed to the client.

See

• GraphQL spec for errors.

Examples

An error thrown in a GraphQL resolver, exposed to the client.

Query:

{
  user(handle: "jaydenseric") {
    name
    email
  }
}

Error thrown in the User.email resolver:

const error = new Error('Unauthorized access to user data.');
error.expose = true;

Response has a 200 HTTP status code, with this payload:

{
  "errors": [
    {
      "message": "Unauthorized access to user data.",
      "locations": [{ "line": 4, "column": 5 }],
      "path": ["user", "email"]
    }
  ],
  "data": {
    "user": {
      "name": "Jayden Seric",
      "email": null
    }
  }
}

---

type ErrorKoaMiddleware

A Koa middleware error may have these special properties for the errorHandler Koa middleware to use to determine how the error appears in the response payload errors array and the response HTTP status code.

Type: object

Property	Type	Description
message	string	Error message. If the error status property >= 500 or the error expose property isn’t true, the message is replaced with Internal Server Error in the response payload errors array.
extensions	object<string, *>?	A map of custom error data that is exposed to the client in the response payload errors array, regardless of the error expose or status properties.
status	number?	Determines the response HTTP status code.
expose	boolean?	Should the original error message be exposed to the client.

See

• GraphQL spec for errors.
• Koa error handling docs.
• http-errors, used by this package and Koa.

Examples

A client error thrown in Koa middleware.

Error constructed manually:

const error = new Error('Rate limit exceeded.');
error.extensions = {
  code: 'RATE_LIMIT_EXCEEDED',
};
error.status = 429;

Error constructed using http-errors:

import createHttpError from 'http-errors';

const error = createHttpError(429, 'Rate limit exceeded.', {
  extensions: {
    code: 'RATE_LIMIT_EXCEEDED',
  },
});

Response has a 429 HTTP status code, with this payload:

{
  "errors": [
    {
      "message": "Rate limit exceeded.",
      "extensions": {
        "code": "RATE_LIMIT_EXCEEDED"
      }
    }
  ]
}

A server error thrown in Koa middleware, not exposed to the client.

Error:

const error = new Error('Database connection failed.');

Response has a 500 HTTP status code, with this payload:

{
  "errors": [
    {
      "message": "Internal Server Error"
    }
  ]
}

A server error thrown in Koa middleware, exposed to the client.

Error:

const error = new Error('Service unavailable due to maintenance.');
error.status = 503;
error.expose = true;

Response has a 503 HTTP status code, with this payload:

{
  "errors": [
    {
      "message": "Service unavailable due to maintenance."
    }
  ]
}

---

type ExecuteOptions

execute Koa middleware options.

Type: object

Property	Type	Description
schema	GraphQLSchema	GraphQL schema.
validationRules	Array?	Validation rules for GraphQL.js validate, in addition to the default GraphQL.js specifiedRules.
rootValue	*?	Value passed to the first resolver.
contextValue	*?	Execution context (usually an object) passed to resolvers.
fieldResolver	Function?	Custom default field resolver.
execute	Function?	Replacement for GraphQL.js execute.
override	ExecuteOptionsOverride?	Override any ExecuteOptions (except override) per request.

Examples

execute middleware options that sets the schema once but populates the user in the GraphQL context from the Koa context each request.

import schema from './schema.mjs';

const executeOptions = {
  schema,
  override: (ctx) => ({
    contextValue: {
      user: ctx.state.user,
    },
  }),
};

---

type ExecuteOptionsOverride

Overrides any ExecuteOptions (except override) per request.

Type: Function

Parameter	Type	Description
context	object	Koa context.

Returns: object — execute middleware options subset.

Examples

An execute middleware options override that populates the user in the GraphQL context from the Koa request context.

const executeOptionsOverride = (ctx) => ({
  contextValue: {
    user: ctx.state.user,
  },
});