fetch-json

A wrapper around Fetch just for JSON

Why would you fetch anything but json? ;)

1) Setup

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@2.1/fetch-json.min.js></script>

node

As a module:

$ npm install fetch-json

then import with the line:

const fetchJson = require('fetch-json');

2) Examples

HTTP GET

Fetch the NASA Astronomy Picture of the Day:

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

HTTP POST

Create a resource for the planet Jupiter:

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

For more examples, see code for Mocha specification cases at: spec-node.js (output)

3) Leverages the Fetch API and node-fetch

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

For comparison, the above POST example to create a planet would be done calling the Fetch API directly with the code:

// Create Jupiter (with Fetch API instead of fetch-json)
const resource = { name: 'Jupiter', position: 5 };
const options = {
   method: 'POST',
   headers: {
      'Content-Type': 'application/json',
      'Accept': 'application/json'
      },
   body: JSON.stringify(resource)
   };
function handleData(data) {
   console.log(data);  //http response body as an object literal
   }
fetch('https://httpbin.org/post', options)
   .then(response => response.json())
   .then(handleData)
   .catch(console.error);

The examples for fetch-json and the Fetch API each produce the same output.

4) Details

The fetch-json module automatically:

1. Serializes the body payload with JSON.stringify().
2. Adds the JSON data type ('application/json') to the HTTP headers.
3. Builds the URL query string from the params object for GET requests.
4. Runs .json() on the response from the promise.
5. Sets credentials to 'same-origin' to support user sessions for frameworks/servers such as Grails, Rails, PHP, Flask, etc.
6. If the response body is HTML or text, it's converted to JSON (makes it easier to handle HTTP error status codes).

5) API

The format for using fetch-json is:

GET

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

POST

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

PUT

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

PATCH

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

DELETE

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

Notes:

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).

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.

Logging

Enable basic logging to the console with:

fetchJson.enableLogger();

Pass in a function to use a custom logger or pass in false to disable logging.

The default console output looks like:
2018-09-12T07:20:12.372Z – "GET" – "https://api.nasa.gov/planetary/apod"

Text to JSON

If the HTTP response body is not JSON (Content-Type is not "application/json" or "text/javascript"), an object containing the body as a string in the bodyText field is created and passed on through the promise.  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><body>Server Error</body></html>'
}

6) Legacy web browsers

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

<script src=https://cdn.jsdelivr.net/npm/promise-polyfill@8.1/dist/polyfill.min.js></script>
<script src=https://cdn.jsdelivr.net/npm/whatwg-fetch@3.0/dist/fetch.umd.min.js></script>

7) Questions or enhancements

Feel free to submit an issue.

MIT License