A small wrapper around unfetch geared specifically for handling JSON

Usage no npm install needed!

<script type="module">
  import isomorphicJsonFetch from '';


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isomorphic-json-fetch 🐕

Useful any time your project needs to consume JSON from some endpoint.

This package is a small wrapper around unfetch geared specifically for fetching JSON and sharing configuration across the application. Specifically:

  • TypeScript support
  • Default method is POST (unless using SWR)
  • Sugar functions for GET/POST/PUT/DELETE methods
  • content-type header is set to application/json
  • Cookies are NOT sent along with the rest of the request (configurable)
  • Request bodies can be anything serializable and will be stringified with JSON.stringify
  • Response bodies are automatically parsed with JSON.parse
  • fetch() will not reject if a non-ok response is received (configurable)
  • Simple differentiation between 2xx responses and non-2xx non-ok responses
  • Exports functions to get and set app-wide configuration
  • Sugar function for simple integration with SWR


npm install isomorphic-json-fetch

Quick start

import { fetch } from 'isomorphic-json-fetch'

const URL = 'api/endpoint';
let res, json, error;

// 1. With zero configuration

({ json } = await fetch(URL)); // <== json will be undefined on non-2xx responses

// 2. With simple error handling and typed JSON

try {
  ({ res, json } = await fetch.get<{ myData: number }>(URL));

  if(!json) return handleErr(`response code outside 200-299: ${res.status}`);

catch(e) {
  // Could be a JSON parse error or a network issue
  handleErr(`fetch failed: ${e}`);

// 3. Explicitly capturing typed JSON from non-2xx responses (e.g. 404, 500)

const configuration = { // <== any configs can also be set globally, see below
  method: 'POST',
  body: { query: 'some-string' }

try {
  ({ json, error } = await fetch<{ myData: number }, { message: string }>(URL, configuration));

  // error is undefined on 2xx responses; json is undefined on non-2xx responses
  if(error) return handleErr(error.message);

catch(e) {
  // Could be a JSON parse error or a network issue
  handleErr(`fetch failed: ${e}`);

// 4. Handling non-2xx responses as exceptions in your own catch block instead

try { doSomethingWith((await<{ myData: number }>(URL, { rejects: true })).json.myData) }
catch(e) {
  // ! Could be a JSON parse error or a network issue OR if the
  // ! status code is not between 200-299!
  handleErr(`fetch failed: ${e}`);

// 5. As a quick little fetcher for SWR

const { data, error } = useSwr(URL, fetch.swr);
// Equivalent to the following:
//                ... = useSwr(URL, (url: string) => fetch(url, { swr: true }));

if(error) return <div>failed to load</div>
if(!data) return <div>loading...</div>
return <div>hello #{data.myData}!</div>

// When using SWR, it's best to set fetch configuration globally (below)

Advanced usage

See unfetch for possible configuration values. Additionally, you can add rejects: true to your config to cause the promise returned by fetch() to reject on non-2xx HTTP responses. By default, the promise returned by fetch() won't reject on HTTP error status even if the response is an HTTP 404 or 500. Instead, it will resolve normally, and it will only reject on network failure or if anything prevented the request from completing. See the unfetch docs for more information.

For use with SWR, add swr: true to your config and return a higher order function manually or just use the fetch.swr sugar (see example above).

If you're using fetch() across many files in a more complex project, you can set a global configuration once and it will be used by all fetch() calls automatically:

import { fetch, setGlobalFetchConfig } from 'isomorphic-json-fetch'

const URL = 'api/endpoint';

// This sets a new default configuration object for all fetch calls
  method: 'DELETE', // ? POST is the default
  credentials: 'include', // ? 'same-origin' by default (no cookies sent!)
  // content-type header is included by default so no need to add it yourself!

// All the following now use the new global config

let { json } = await fetch(URL); // <== Sends a DELETE request

// You can always override default/global config by providing your own
({ json } = await fetch(URL, { // <== Sends a PUT request
  method: 'PUT',
  // `headers` and `credentials` keys were not overridden, so their values are
  // inherited from global config like normal

// This will ignore any errors thrown by `JSON.parse()`
({ json } = await fetch(URL, { method: 'GET', ignoreParseErrors: true }));

json === undefined // true

// TypeScript support for defining json return type and error return type
({ json } = await fetch.get<'technically valid JSON', { error: string }>(URL));

// Also, if you want to use the normal unfetch/node-fetch isomorphically, like
// for stream support in Node, it can be imported via `unfetch`
import { fetch, unfetch } from 'isomorphic-json-fetch'

Instead of passing method choice through a configuration option, this package provides several sugar functions:

import { fetch } from 'isomorphic-json-fetch'

const { json: get }  = await fetch.get('/app?t=1');
const { json: post } = await'/app?t=2', { body: { create: true }});
const { json: put }  = await fetch.put('/app?t=3', { body: { newData: 'yes' }});
const { json: del }  = await fetch.delete('/app?t=4');


Documentation can be found under docs/ and can be built with npm run build-docs.

Supporting and Contributing

New issues and pull requests are always welcome and greatly appreciated! 🤩 But that's not the only way to contribute! Just as well, you can star 🌟 this project to let me know you found it useful! Thank you for your support ✊🏿

This repository uses a CI/CD semantic-release pipeline for vetting PRs and publishing releases. Be sure to checkout the develop branch (not main) and, when you're ready, fearlessly submit your PR against develop. The pipeline will take care of the rest 🚀🚀🚀

NPM Scripts

Run npm run list-tasks locally to see which of the following scripts are available for this project.

Using these scripts requires a linux-like development environment. None of the scripts are likely to work on non-POSIX environments. If you're on Windows, use WSL.


  • npm run repl to run a buffered TypeScript-Babel REPL
  • npm test to run the unit tests and gather test coverage data
    • Look for HTML files under coverage/
  • npm run check-build to run the integration tests
  • npm run check-types to run a project-wide type check
  • npm run test-repeat to run the entire test suite 100 times
    • Good for spotting bad async code and heisenbugs
    • Uses __test-repeat NPM script under the hood
  • npm run dev to start a development server or instance
  • npm run generate to transpile config files (under config/) from scratch
  • npm run regenerate to quickly re-transpile config files (under config/)


  • npm run clean to delete all build process artifacts
  • npm run build to compile src/ into dist/, which is what makes it into the published package
  • npm run build-docs to re-build the documentation
  • npm run build-externals to compile external-scripts/ into external-scripts/bin/
  • npm run build-stats to gather statistics about Webpack (look for bundle-stats.json)


  • npm run start to start a production instance


  • npx sort-package-json to consistently sort package.json
  • npx npm-force-resolutions to forcefully patch security audit problems

Package Details

You don't need to read this section to use this package, everything should "just work"!

This is a dual UMD (CJS2)/ES module package. That means this package exposes both UMD+CJS2 and ESM entry points and can be used in most JavaScript environments (browsers, any current or LTS Node version, etc).

Loading this package via require(...) will cause Node and modern browsers to use the CJS2 bundle entry point, disable tree shaking in Webpack 4, and lead to larger bundles in Webpack 5. Alternatively, loading this package via import { ... } from ... or import(...) will cause Node and modern browsers to use the ESM entry point in versions that support it, in Webpack, and in the browser. Using the import syntax is the modern, preferred choice.

For backwards compatibility with Webpack 4 and Node versions < 14, package.json retains the module key, which points to the ESM entry point, and the main key, which points to both the ESM and CJS2 entry points implicitly (no file extension). For Webpack 5 and Node versions >= 14, package.json includes the exports key, which points to both entry points explicitly.

Though package.json includes { "type": "commonjs"}, note that the ESM entry points are ES module (.mjs) files. package.json also includes the sideEffects key, which is false for optimal tree shaking, and the types key, which points to a TypeScript declarations file.

This package does not maintain shared state and so does not exhibit the dual package hazard. However, setting global configuration may not actually be "globally" recognized by third-party code importing this package.