End-to-end typing for REST APIs with TypeScript

Motivation

Read the blog post

Benefits

• End-to-end typing. Share request and response types between your client and server for ease of use and peace of mind.
• Unopinionated. Works with any new or existing REST API.
• Universal. Can support any server framework or REST client.
• Lightweight Weightless. Client and server implementations add no runtime code--It's Just Types™.
• Use existing syntax. Declare and call your routes the same way you always have.
• Great for private APIs. Keep API clients across your organization in sync with the latest changes.
• Great for public APIs. Create a RESTyped definition so TypeScript users can consume your API fully typed.
• Easy to learn and use. Start using RESTyped in less than one minute per route.

How to use it

RESTyped is a specification (see below). You can use these server and client packages along with a RESTyped defintion file to declare and consume APIs in a type-safe manner:

• restyped-axios - Client wrapper for Axios to consume RESTyped APIs
• restyped-express-async - Server wrapper for express to deliver RESTyped APIs using promises
• restyped-hapi - Server wrapper for Hapi.js routes to deliver RESTyped APIs

You can help make RESTyped more useful by implementing support in your favorite server framework or HTTP client!

RESTyped requires TypeScript 2.4 or higher.

Specification

It's very easy to get started with RESTyped. Just follow a few steps to type your existing API or create a new typed API:

• Your API should be defined in one interface, exported as {my_api_name}API from a file ending in .d.ts
• Each route is a top level key in the interface. You should exclude any prefixes like /api/.
• Each route can have up to one key per valid HTTP method:
  • GET, POST, PUT, PATCH, DELETE, HEAD or OPTIONS
• Each HTTP method can have one or more of the following keys:
  • params: Route params in the URL (e.g. /users/:id would have id as a param)
  • query: Query string params, typically used in GET requests (e.g. req.query in express)
  • body: JSON body object (e.g. req.body in express or data object in an axios request)
  • response: The route's JSON response

Also see the spec implementation base defintions.

Example: my-social-api.d.ts

interface User {
  // Model inteface--could be imported from another file
  email: string
  name: string
  gender: 'Male' | 'Female' | 'Other'
}

export interface MySocialAPI {
  '/users': {
    // Route name (without prefix, if you have one)
    GET: {
      // Any valid HTTP method
      query: {
        // Query string params (e.g. /me?includeProfilePics=true)
        includeProfilePics?: boolean
      }
      response: User[] // JSON response
    }
  }

  '/user/:id/send-message': {
    POST: {
      params: {
        // Inline route params
        id: string
      }
      body: {
        // JSON request body
        message: string
      }
      response: {
        // JSON response
        success: boolean
      }
    }
  }
}

Full-Stack Example

1. Define your API

food-delivery-api.d.ts

export interface FoodDeliveryAPI {
  '/me/orders': {
    POST: {
      body: {
        foodItemIds: number[]
        address: string
        paymentMethod: 'card' | 'cash'
      }
      response: {
        success: boolean
        eta?: string
      }
    }
  }

  // ...other routes...
}

2. Declare the API via express

import RestypedRouter from 'restyped-express-async'
import { FoodDeliveryAPI } from './food-delivery-api'
import * as express from 'express'

const app = express()

const apiRouter = express.Router()
app.use('/api', apiRouter)

const router = RestypedRouter<FoodDeliveryAPI>(apiRouter)

router.post('/me/orders', async req => {
  // Will not compile if you attempt to access an invalid body property
  const {
    foodItemIds, // number[]
    address, // string
    paymentMethod // 'card' | 'cash'
  } = req.body

  const success = await OrderModel.order(foodItemIds, address, paymentMethod)

  // Will not compile if returned value is not of type {success: boolean}
  return { success }
})

3. Consume the API via axios

import axios from 'restyped-axios'
import { FoodDeliveryAPI } from './food-delivery-api'

const api = axios.create<FoodDeliveryAPI>({
  baseURL: 'https://fooddelivery.com/api/'
})

async function order() {
  // Will not compile if you pass incorrectly typed body params
  const res = await api.post('/me/orders', {
    foodItemIds: [142, 788],
    address: '1601 Market St, Phiadelphia, PA 19103',
    paymentMethod: 'cash'
  })

  // TypeScript knows that res.data is of type {success: boolean, eta?: string}
  const { success, eta } = res.data
}

What RESTyped isn't

• A replacement for API docs. A RESTyped spec will help you get the routes and types right, but doesn't provide any context or explanation of your API.

Popular APIs to try out

• Giphy API: restyped-giphy-api