Fetch API mixin to set a default base URL and options. Functional and immutable.

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FetchDefaults.js is a mixin for the Fetch APIfetch for browsers and Node.js that allows you to set a base URL (to then make relative requests) and default options (such as headers) for fetch calls. It's functional and immutable, in that it doesn't modify any objects given to it.


npm install fetch-defaults

FetchDefaults.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).


Pass the native fetch function and a base URL and/or options to fetchDefaults:
var fetchDefaults = require("fetch-defaults")

var apiFetch = fetchDefaults(fetch, "https://example.com", {
  headers: {Authorization: "Bearer 42"}

Then use the returned function as you would before:
var res = apiFetch("/models", {method: "POST", body: "John"})

The above will then call the original function with a URL of https://example.com/models and a new merged options object. Options are merged recursively, so even nested objects, like headers, will work. The object you pass in will not be modified, just in case you were worried.
If you don't need to set any options, omit the second argument:
var apiFetch = fetchDefaults(fetch, "https://example.com")
var res = apiFetch("/models", {method: "POST", body: "John"})

Likewise, if you don't need a base URL, pass only options:
var apiFetch = fetchDefaults(fetch, {
  headers: {Authorization: "Bearer 42"}

var res = apiFetch("https://example.com/models", {
  method: "POST", body: "John"


Browsers have the Fetch API available at window.fetch:
var fetchDefaults = require("fetch-defaults")
var apiFetch = fetchDefaults(fetch, "https://example.com")


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.jsfetch-off or node-fetchnode-fetch:
var fetch = require("fetch-off")
var fetchDefaults = require("fetch-defaults")
var apiFetch = fetchDefaults(fetch, "https://example.com")


FetchDefaults.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 Möllmoll typed this and the code.
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monday supported the engineering work.
If you find FetchDefaults.js needs improving, please don't hesitate to type to me now at andri@dot.eeemail or create an issue onlineissues.