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Fetch API mixin for stringifying JSON and setting Content-Type if unset. Functional and immutable.
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Fetch JSONify is a mixin for the Fetch API for browsers and Node.js that stringifies JSON and sets the Content-Type header if not given. It's functional and immutable, in that it doesn't modify any properties given to it.


npm install fetch-jsonify

FetchJSONify.js follows semantic versioning, so feel free to depend on its major version with something like >= 1.0.0 < 2 (a.k.a ^1.0.0).


Wrap the native fetch function with the one from FetchJSONify.js:

var fetch = require("fetch-jsonify")(global.fetch)

Then pass any value or object you'd like stringified under the json property:

fetch("/models", {method: "POST", json: {name: "John"}})

That property will be stringified with JSON.stringify and passed on to the original fetch function under the body property. The Content-Type header will be set to application/json if it's not set.


To set a custom Content-Type header, just pass it as you normally would:

fetch("/models", {
  method: "POST",
  headers: {"Content-Type": "application/vnd.model+json"},
  json: {name: "John"}


Browsers have the Fetch API available at window.fetch:

var fetch = require("fetch-jsonify")(window.fetch)
fetch("/models", {method: "POST", json: {name: "John"}})


Node.js doesn't have a built-in implementation of the Fetch API, but you can use any library with a compatible interface, such as my Fetch/Off.js or node-fetch:

var fetch = require("fetch-jsonify")(require("node-fetch"))
fetch("/models", {method: "POST", json: {name: "John"}})


FetchJSONify.js is released under a Lesser GNU Affero General Public License, which in summary means:

  • You can use this program for no cost.
  • You can use this program for both personal and commercial reasons.
  • You do not have to share your own program's code which uses this program.
  • You have to share modifications (e.g. bug-fixes) you've made to this program.

For more convoluted language, see the LICENSE file.


Andri Möll typed this and the code.
Monday Calendar supported the engineering work.

If you find FetchJSONify.js needs improving, please don't hesitate to type to me now at or create an issue online.

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