Typeful Fetch

A fetch builder with type support

Usage

First, you'll need to define some Descriptors to describe your fetch endpoints. Then just call createClient with your descriptors and you're good to go! See examples below.

See references for more details.

Examples

import {
  createClient,
  RouterDescriptor,
  HandlerDescriptor
} from 'typeful-fetch'

type D = RouterDescriptor<{
  '/': {
    GET: HandlerDescriptor<{
      querystring: {
        aaa: string
      }
      response: {
        200: {
          bbb: string
        }
      }
    }>
    POST: HandlerDescriptor<{
      body: {
        ccc: string
      }
      response: {
        200: {
          ddd: string
        }
      }
    }>
  }
  '/misc': RouterDescriptor<{
    '/': {
      PUT: HandlerDescriptor<{
        body: {
          eee: string
        }
        response: {
          200: {
            fff: string
          }
        }
      }>
    }
    '/hello': {
      GET: HandlerDescriptor<{
        response: {
          200: {
            ggg: string
          }
        }
      }>
    }
  }>
}>

const client = createClient<D>('http://localhost:3000/')
client.$get.query({ aaa: '123' }).fetch() // Promise<{ bbb: string; }>
client.$post.body({ ccc: '456' }).fetch() // Promise<{ ddd: string; }>
client.misc.$put.body({ eee: '789' }).fetch() // Promise<{ fff: string; }>
client.misc.hello.$get.fetch() // Promise<{ ggg: string; }>

More examples could be found in the unit tests.

References

Descriptors

Descriptors are used to describe your fetch endpoints. They are used to generate a client with type support.

We only have two types of descriptors: RouterDescriptor and HandlerDescriptor.

RouterDescriptor

type Route = RouterDescriptor<any> | Record<string, HandlerDescriptor<any>>
interface RouterDescriptor<Routes extends Record<string, Route>> {...}

RouterDescriptor is used to describe a router. It takes a generic type Routes which is a record of routes. Each route can be either a RouterDescriptor or a record of method to HandlerDescriptor.

Also, route with a prefix / will have that prefix removed. Thus, the following two descriptors are equivalent:

type D1 = RouterDescriptor<{
  '/hello': {
    GET: HandlerDescriptor<{ response: { 200: { a: string } } }>
  }
}>
type D2 = RouterDescriptor<{
  hello: {
    GET: HandlerDescriptor<{ response: { 200: { a: string } } }>
  }
}>

But we recommend using the first one, because it's more explicit.

Notice that we have special handling for the / route. It is used to describe the root route of a router. If exists, it should be a record of method to HandlerDescriptor. Otherwise, the type inference is not promised to succeed.

HandlerDescriptor

interface EndpointSchema<
  Body,
  Query,
  Params,
  Headers,
  Response extends Record<number, any>
> {
  body?: Body
  querystring?: Query
  params?: Params
  headers?: Headers
  response?: Response
}

interface HandlerDescriptor<Schema extends EndpointSchema<any, any, any, any, any>> {...}

HandlerDescriptor is used to describe a handler. Please notice that handlers have nothing to do with the path and method; they are just used to describe the schema of the endpoint.

To have the generated fetch return a promise with the correct type, you need to specify the response field in the schema. The key of the response field should be the status code of the response, and the value should be the type of the response body. Thus, you should at least specify the response.200 field.

API

createClient

function createClient<R extends RouterDescriptor<any>>(
  path: string,
  options: RequestInit = {}
)

createClient takes a RouterDescriptor as generic parameter and returns a client with type support.

Parameters:

• path: the base path of the client
• options: the default options of the client, which'll be deep merged into every fetch request

Returns:

A client with type support, which have the intuitive structure corresponding to the given RouterDescriptor.

Generally speaking, you will have to use client.some.path.to.the.api.$method to get a ClientHandler, using which you could form the actual fetch request. The expression given above will be mapped into an URL ${path}/some/path/to/the/api and a method method, which is saved in the ClientHandler that you got.

Also, you could use client.$unsafe to get a client with identical path and options, but have type checking turned off. Use this if you want to use the client to fetch endpoints that are not described by the RouterDescriptor.

ClientHandler

Methods:

• body: set the body of the request
• query: set the querystring of the request
• params: set the params of the request
• headers: set the headers of the request
• fetch: form and fire the actual fetch request

Notice that query is serialized using the qs package, and params are implemented by simple doing string replacement stuff. Pay attention when using these two methods.

Please refer to the code for more details.