A wrapper around Fetch just for JSON (written in TypeScript)


2612.6.42 months ago7 years agoMinified + gzip package size for fetch-json in KB




A wrapper around Fetch just for JSON (written in TypeScript)

License:MIT npm Size Vulnerabilities Build

Why would you fetch anything but json? ;)

1) Make REST Easy

fetch-json automatically:

  1. Converts the HTTP response to JSON if it's not already JSON (especially convenient for HTTP errors)
  2. Serializes the body payload with JSON.stringify()
  3. Adds the application/json HTTP header to set the data type
  4. Appends the GET params object items to the URL
  5. Runs .json() on the response
  6. Sets credentials to 'same-origin' (support user sessions in Grails, Rails, PHP, Django, Flask, etc.)

fetch-json is ideal for a JAMstack architecture where "dynamic programming during the request/response cycle is handled by JavaScript, running entirely on the client".

2) Setup

Web browser

In a web page:

<script src=fetch-json.min.js></script>

or from the jsdelivr.com CDN:

<script src=https://cdn.jsdelivr.net/npm/fetch-json@2.6/dist/fetch-json.min.js></script>

Node.js server

Install package for node:

$ npm install node-fetch fetch-json

and then import:

import { fetchJson } from 'fetch-json';

or for older CommonJS modules use:

const { fetchJson } = require('fetch-json');  //deprecated

3) Examples


Fetch the NASA Astronomy Picture of the Day:

const url =    'https://api.nasa.gov/planetary/apod';
const params = { api_key: 'DEMO_KEY' };
const handleData = (data) =>
   console.log('The NASA APoD for today is at:', data.url);
fetchJson.get(url, params).then(handleData);

Example output:

> The NASA APoD for today is at:
> https://apod.nasa.gov/apod/image/2107/LRVBPIX3M82Crop1024.jpg


Create a resource for the planet Jupiter:

// Create Jupiter
const resource = { name: 'Jupiter', position: 5 };
const handleData = (data) =>
   console.log('New planet:', data);  //http response body as an object literal
fetchJson.post('https://httpbin.org/post', resource)

For more examples, see the Mocha specification suite:
spec/node.spec.js (Mocha output for each build under Run npm test)

To see a website that incorporates fetch-json, check out DataDashboard:
data-dashboard.js.org 📊

4) Examples Using async/await


Fetch the NASA Astronomy Picture of the Day:

const show = async () => {
   const url =    'https://api.nasa.gov/planetary/apod';
   const params = { api_key: 'DEMO_KEY' };
   const data =   await fetchJson.get(url, params);
   console.log('The NASA APoD for today is at: ' + data.url);


Create a resource for the planet Jupiter:

// Create Jupiter
const create = async (resource) => {
   const data = await fetchJson.post('https://httpbin.org/post', resource);
   console.log('New planet:', data);  //http response body as an object literal
create({ name: 'Jupiter', position: 5 });

5) Leverages the Fetch API and node-fetch

fetch-json calls the native Fetch API if in a web browser and calls node-fetch if running on node.

For comparison, the POST example in section 3) Examples to create a planet would be done calling the Fetch API directly with the code:

// Create Jupiter (WITHOUT fetch-json)
const resource = { name: 'Jupiter', position: 5 };
const options = {
   method: 'POST',
   headers: {
      'Content-Type': 'application/json',
      'Accept': 'application/json',
   body: JSON.stringify(resource),
const handleData = (data) =>
   console.log(data);  //http response body as an object literal
fetch('https://httpbin.org/post', options)
   .then(response => response.json())

The example with fetch-json and the example without fetch-json each produce the same output.

6) API

API — HTTP Request

The format for using fetch-json is:


fetchJson.get(url, params, options).then(callback);


fetchJson.post(url, resource, options).then(callback);


fetchJson.put(url, resource, options).then(callback);


fetchJson.patch(url, resource, options).then(callback);


fetchJson.delete(url, resource, options).then(callback);


  1. Only the url parameter is required.  The other parameters are optional.
  2. The params object for fetchJson.get() is converted into a query string and appended to the url.
  3. The resource object is turned into the body of the HTTP request.
  4. The options parameter is passed through to the Fetch API (see the init documentation on MDN).
  5. options is enhanced with a boolean setting for strictErrors mode (default false) that throws an error to .catch() whenever the HTTP response status is 400 or higher.

Dynamic HTTP method

If you need to programmatically set the method, use the format:

fetchJson.request(method, url, data, options).then(callback);

Where method is 'GET', 'POST', 'PUT', 'PATCH', or 'DELETE', and data represents either params or resource.

API — Logging

Enable basic logging to the console with:


To use a custom logger, pass in a function that accepts 9 parameters to log. To disable logging, pass in false.

To get an array containing the names of the parameters:


The default console output looks like:
2018-09-12T07:20:12.372Z – "request" - "GET" – "api.nasa.gov" – "https://api.nasa.gov/planetary/apod"
2018-09-12T07:20:13.009Z – "response" - "GET" – "api.nasa.gov" – "https://api.nasa.gov/planetary/apod" - true - 200 - "OK" - "application/json"

7) Response Text Converted to JSON

The HTTP response body is considered to be JSON if the Content-Type is "application/json" or "text/javascript".  If the HTTP response body is not JSON, fetch-json passes back through the promise an object with a bodyText string field containing response body text.

In addition to the bodyText field, the object will have the fields: ok, status, statusText, and contentType.

For example, an HTTP response for an error status of 500 would be converted to an object similar to:

   ok:          false,
   status:      500,
   statusText:  'INTERNAL SERVER ERROR',
   contentType: 'text/html; charset=utf-8',
   bodyText:    '<!doctype html><html lang=en><body>Server Error</body></html>',

With fetch-json, you know the response body will always be passed back to you as a simple object literal.

8) Base Options

Use fetchJson.setBaseOptions() to configure options to be used on future fetchJson requests.

The example below sets the Authorization HTTP header so it is sent on the subsequent GET and DELETE requests:

fetchJson.setBaseOptions({ headers: { Authorization: 'Basic WE1MIGlzIGhpZGVvdXM=' } });
fetchJson.get('https://dnajs.org/api/books/').then(display);  //with auth header
fetchJson.delete('https://dnajs.org/api/books/3/');           //with auth header

To have multiple base options available at the same time, use the FetchJson class to instantiate multiple copies of fetchJson:

import { FetchJson } from 'fetch-json';
const fetchJsonA = new FetchJson({ headers: { From: 'aaa@example.com' } }).fetchJson;
const fetchJsonB = new FetchJson({ headers: { From: 'bbb@example.com' } }).fetchJson;
fetchJsonA.get('https://dnajs.org/api/books/').then(display);  //from aaa@example.com
fetchJsonB.delete('https://dnajs.org/api/books/3/');           //from bbb@example.com

9) TypeScript Declarations

The TypeScript Declaration File file is fetch-json.d.ts in the dist folder.

The declarations provide type information about the API. For example, the fetchJson.post() function returns a Promise for a FetchResponse:

fetchJson.post(url: string, resource?: RequestData,
   options?: FetchOptions): Promise<FetchResponse>

10) Legacy Web Browsers

To support really old browsers, include polyfills for Promise and Fetch API:

<script src=https://cdn.jsdelivr.net/npm/promise-polyfill@8.2/dist/polyfill.min.js></script>
<script src=https://cdn.jsdelivr.net/npm/whatwg-fetch@3.6/dist/fetch.umd.min.js></script>

Note: JSDOM does not include fetch, so you need to add a polyfill.  See usage of whatwg-fetch in spec/jsdom.spec.js and gulpfile.js.

10) Contributor Notes

To be a contributor, fork the project and run the commands npm install and npm test on your local clone.  Make your edits and rerun the tests.  Pull requests welcome.

"Stop trying to make fetch happen without #fetchJson!"

Feel free to submit questions at:

MIT License

If you find any bugs or have a feature request, please open an issue on github!

The npm package download data comes from npm's download counts api and package details come from npms.io.