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A JavaScript library for an error class for use with the Fetch API.
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NPM version

FetchError.js is an error class for use with the Fetch API.
It's based on StandardHttpError.js.


npm install fetch-error

FetchError.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).


var FetchError = require("fetch-error")

function errorify(res) {
  if (res.status >= 400 && res.status < 600)
    throw new FetchError(res.status, res.statusText, {response: res})
    return res

var res = fetch("/").then(errorify)

Should the response be unsuccessful, the promise will be rejected with FetchError Such a pattern of separating success flows from failures is very handy: in the response resolve handlers you know all went well and don't have to double check for errors every time.

You can also later detect an erroneous response from other errors, such as bugs, through instanceof:

res.catch(function(err) {
  if (err instanceof FetchError) console.error(err.message)
  else throw err

For a library that does the above and slightly more, see FetchThrow.js.


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

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