📘️ openapi-typescript-fetch

A typed fetch client for openapi-typescript

Install

1npm install openapi-typescript-fetch

Or

1yarn add openapi-typescript-fetch

Features

Supports JSON request and responses

• ✅ OpenAPI 3.0
• ✅ Swagger 2.0

Usage

Generate typescript definition from schema

1npx openapi-typescript https://petstore.swagger.io/v2/swagger.json --output petstore.ts
2
3# 🔭 Loading spec from https://petstore.swagger.io/v2/swagger.json…
4# 🚀 https://petstore.swagger.io/v2/swagger.json -> petstore.ts [650ms]

Typed fetch client

1import { Fetcher } from 'openapi-typescript-fetch'
2
3import { paths } from './petstore'
4
5// declare fetcher for paths
6const fetcher = Fetcher.for<paths>()
7
8// global configuration
9fetcher.configure({
10  baseUrl: 'https://petstore.swagger.io/v2',
11  init: {
12    headers: {
13      ...
14    },
15  },
16  use: [...] // middlewares
17})
18
19// create fetch operations
20const findPetsByStatus = fetcher.path('/pet/findByStatus').method('get').create()
21const addPet = fetcher.path('/pet').method('post').create()
22
23// fetch
24const { status, data: pets } = await findPetsByStatus({
25  status: ['available', 'pending'],
26})
27
28console.log(pets[0])

Typed Error Handling

A non-ok fetch response throws a generic ApiError

But an Openapi document can declare a different response type for each status code, or a default error response type

These can be accessed via a discriminated union on status, as in code snippet below

1const findPetsByStatus = fetcher.path('/pet/findByStatus').method('get').create()
2const addPet = fetcher.path('/pet').method('post').create()
3
4try {
5  await findPetsByStatus({ ... })
6  await addPet({ ... })
7} catch(e) {
8  // check which operation threw the exception
9  if (e instanceof addPet.Error) {
10    // get discriminated union { status, data } 
11    const error = e.getActualType()
12    if (error.status === 400) {
13      error.data.validationErrors // only available for a 400 response
14    } else if (error.status === 500) {
15      error.data.errorMessage // only available for a 500 response
16    } else {
17      ...
18    }
19  }
20}

Middleware

Middlewares can be used to pre and post process fetch operations (log api calls, add auth headers etc)

1
2import { Middleware } from 'openapi-typescript-fetch'
3
4const logger: Middleware = async (url, init, next) => {
5  console.log(`fetching ${url}`)
6  const response = await next(url, init)
7  console.log(`fetched ${url}`)
8  return response
9}
10
11fetcher.configure({
12  baseUrl: 'https://petstore.swagger.io/v2',
13  init: { ... },
14  use: [logger],
15})
16
17// or
18
19fetcher.use(logger)

Utility Types

• OpArgType - Infer argument type of an operation
• OpReturnType - Infer return type of an operation
• OpErrorType - Infer error type of an operation
• FetchArgType - Argument type of a typed fetch operation
• FetchReturnType - Return type of a typed fetch operation
• FetchErrorType - Error type of a typed fetch operation
• TypedFetch - Fetch operation type

1import { paths, operations } from './petstore'
2
3type Arg = OpArgType<operations['findPetsByStatus']>
4type Ret = OpReturnType<operations['findPetsByStatus']>
5type Err = OpErrorType<operations['findPetsByStatus']>
6
7type Arg = OpArgType<paths['/pet/findByStatus']['get']>
8type Ret = OpReturnType<paths['/pet/findByStatus']['get']>
9type Err = OpErrorType<paths['/pet/findByStatus']['get']>
10
11type FindPetsByStatus = TypedFetch<operations['findPetsByStatus']>
12
13const findPetsByStatus = fetcher.path('/pet/findByStatus').method('get').create()
14
15type Arg = FetchArgType<typeof findPetsByStatus>
16type Ret = FetchReturnType<typeof findPetsByStatus>
17type Err = FetchErrorType<typeof findPetsByStatus>

Utility Methods

• arrayRequestBody - Helper to merge params when request body is an array see issue

1
2const body = arrayRequestBody([{ item: 1}], { param: 2})
3
4// body type is { item: number }[] & { param: number }

Changing the baseUrl at runtime

The baseUrl can be configured with a function that returns the url at runtime

1fetcher.configure({
2  baseUrl: () => getBaseUrl(...)
3})

It can also be overriden per method invocation

1await findPetsByStatus(
2  { status: ['available', 'pending'] },
3  { baseUrl: "https://staging.petstore.swagger.io/v2" }
4)

Happy fetching! 👍