---

“it's just native fetch, but easier.”

~ probably someone

Features

• Ultra tiny (~700 bytes)
• Uses native fetch, but lets you skip the boilerplate:
  • Parses responses
  • Serializes object payloads
• Actually throws HTTP status errors (unlike native fetch)
• 100% native fetch options
• Fully typed/TypeScript support

Installation

npm install itty-fetcher

then...

import { fetcher } from 'itty-fetcher'

Examples

GET - fetcher vs. fetch

// itty-fetcher
const kittens = await fetcher().get('https://api.kittens.com')


// native fetch
const kittens = await fetch('https://api.kittens.com').then(response => response.json())

POST - fetcher vs. fetch

// itty-fetcher
await fetcher().post('https://api.kittens.com', ['Fluffy', 'Mittens', 'Halsey'])


// native fetch
await fetch('https://api.kittens.com', {
  method: 'POST',
  headers: {
    'content-type': 'application-json',
  },
  body: JSON.stringify(['Fluffy', 'Mittens', 'Halsey']),
})

Preconfigure your API

// define your base fetcher
const kittensAPI = fetcher({
                     base: 'https://api.kittens.com',
                     headers: {
                       'Authorization': 'Token FooBarBaz',
                     }
                   })

// then call it!
const names = await kittensAPI.get('/names')

Error Handling - fetcher vs. fetch

// itty-fetcher
const data = await fetcher()
                     .get('https://api.kittens.com')
                     .catch(({ status, error }) => {
                       console.error(`Error code ${status}: ${error}`)
                     })


// or to capture the error
const { error, data } = await fetcher()
                                .get('https://api.kittens.com')
                                .then(data => ({ data }))
                                .catch(error => ({ error }))


// native fetch
const data = await fetch('https://api.kittens.com')
                     .then(response => {
                       if (!response.ok) {
                         const error = new Error(response.statusText)
                         error.status = response.status
                         throw error
                       }
                     })
                     .then(response => response.json())
                     .catch(({ status, error }) => {
                       console.error(`Error code ${status}: ${error}`)
                     })

Use any native fetch options (passthrough)

await fetcher()
        .post('https://api.kittens.com', { foo: 'bar' }, {
          credentials: 'same-origin',
          headers: {
            'Authorization': 'Token FooBarBaz',
          },
        })

---

Why yet another fetching library?

We've all done this countless times in our apps...

We want to make a nice, lightweight app that (of-course) talks to some API. We could import a full-featured fetch library like axios, but we want to keep our bundle size down, right?

So we just write some basic native fetch statements. That's not hard... we've tread this ground before! Of course as the project grows a bit, we start to become bothered by the repeated boilerplate of setting headers, checking for errors, translating response bodies, etc.

So what do we do?

Why, we write a little abstraction layer of course! Just like this one, but probably a bit bigger.

So who is this for?

This is not a kitchen-sink sort of library. It will intentionally not cover every edge case. By only handling a variety of the most common use-cases, we can keep the bundle size down to [likely] smaller than the code you would have written yourself, making it a no-brainer for easy inclusion into your projects.

Need more advanced fetch handling? Perhaps try a different library!

Notes

itty-fetcher wraps the existing native fetch method, so it will work in any environment that supports fetch (including modern web browsers, Cloudflare Workers/Pages, SvelteKit, and Node v18+). Note that we depend on web APIs including Request, FormData and URL. Almost all environments that support fetch will also support these APIs, but if you need to support older browsers or other environements, you may need to include a polyfill. Note if you're using Node you need to be running v18 or newer.

API

fetcher(options?: FetcherOptions): FetcherType

Returns a fetcher object, with method calls (like .get, .post, etc) mapped to fetch commands.

Option	Type(s)	Default	Description
autoParse	boolean	true	By default, all responses are parsed to JSON/text/etc. To access the Response directly, set this to false.
base	string	'' (an empty string)	Use this to prefix all future fetch calls, for example { base: "https://api.foo.bar/v1" }, allows future calls such as fetcher.get('/kittens/14') to work by automatically prepending the base URL.
fetch	typeof fetch	undefined	An optional implementation of fetch that will be used instead of the built-in fetch on all requests. This is useful when your may need to work with a modified version of fetch, like SvelteKit's load function.
handleResponse	(response: Response) => any	undefined	An optional method to take over the response-handling (and throwing) of itty-fetcher. Using this will disregard the autoParse flag. This option allows for a transform to split responses into { data, error } shapes, for instance, to better align with await syntax.
transformRequest	(request: RequestLike) => RequestLike	undefined	An optional method that allows for transforming a request before it is sent. This is useful for adding headers, etc. The method is passed the request object, and should return the request object (or a new one). See below for examples.

RequestLike matches the following signature:

type RequestLike = RequestInit & {
  method: string // method is required
  headers: HeadersInit // headers are populated with { 'Content-Type': 'application/json' } if not set
  url: string // url is required and is the fully qualified URL
}

transformRequest examples

// Add a header to every request
fetcher({
  transformRequest(req) {
    req.headers['Authorization'] = token
    return req
  },
})

// Add a query param to every request
fetcher({
  transformRequest(req) {
    const url = new URL(req.url)
    url.searchParams.set('message', 'hello world')
    req.url = url.toString()
    return req
  },
})

// Only add a header on a "/admin" route
fetcher({
  transformRequest(req) {
    const url = new URL(req.url)
    if (url.pathname.startsWith('/admin')) {
      req.headers['Authorization'] = token
    }
    return req
  },
})

// Change the origin of a URL only in dev mode
fetcher({
  transformRequest(req) {
    if (dev) {
      req.url = req.url.replace('prod.example.com', 'dev.example.com')
    }
    return req
  },
})

// Only apply a token on a specific domain
fetcher({
  transformRequest(req) {
    if (req.url.startsWith("https://api.example.com") {
      req.headers["Authorization"] = `Bearer ${token}`
    }
    return req
  }
})

// Util function to inject a user auth token into a request
function api_client(token: string) {
  return fetcher({
    base: 'https://api.example.com',
    transformRequest(req) {
      req.headers['Authorization'] = token
      return req
    },
  })
}

// Somewhere else...
const token = read_jwt(jwt_cookie)
const api = api_client(token)
api.get('/foo')

fetcher().{method}(url, payload, options)

Each method call maps to the corresponding HTTP method (in uppercase) with the following signature:

Example

fetcher().patch('https://foo.bar', { value: 2 })
// sends PATCH to https://foo.bar with payload of { value: 2 }

Parameter	Type(s)	Required?	Description
url	string	yes	This will be appended to the fetcher.base option (if found) to make the request
payload	string, number, object, any[], URLSearchParams	no*	This will be attached to the request body (or sent as query params for GET requests). If using options, this param spot should be retained with undefined.
options	object	no	These are native fetch options to be sent along with the request, and will be merged with options created internally.

---

Special Thanks

I have to thank my friends and colleagues that helped me through the idea itself, implementation details, and importantly... made it possible for me to muck through making this a TS-first library. Huge thanks for that!!

Contributors

As always, these are the real heroes!

@danawoodman - For a truly amazing amount of work with me on this project, including (but not limited to) build improvements, testing improvements, query param (GET) support, and the incredibly powerful transformRequest feature, which unlocks future plugin support potential! Huge thanks, Dana!! :)