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A tiny (~1.9KB g-zipped) wrapper built around fetch with an intuitive syntax.

f[ETCH] [WR]apper

Wretch 2.3 is now live 🎉 ! Please have a look at the releases and the changelog after each update for new features and breaking changes. If you want to try out the hot stuff, please look into the dev branch.
And if you like the library please consider becoming a sponsor ❤️.


wretch is a small wrapper around fetch designed to simplify the way to perform network requests and handle responses.

  • 🪶 Small - core is less than 2KB g-zipped
  • 💡 Intuitive - lean API, handles errors, headers and (de)serialization
  • 🧊 Immutable - every call creates a cloned instance that can then be reused safely
  • 🔌 Modular - plug addons to add new features, and middlewares to intercept requests
  • 🧩 Isomorphic - compatible with modern browsers, Node.js 14+ and Deno
  • 🦺 Type safe - strongly typed, written in TypeScript
  • Proven - fully covered by unit tests and widely used
  • 💓 Maintained - alive and well for many years

Table of Contents


Because having to write a second callback to process a response body feels awkward.

Fetch needs a second callback to process the response body.

  .then(response => response.json())
  .then(json => {
    //Do stuff with the parsed json

Wretch does it for you.

// Use .res for the raw response, .text for raw text, .json for json, .blob for a blob ...
  .json(json => {
    // Do stuff with the parsed json

Because manually checking and throwing every request error code is tedious.

Fetch won’t reject on HTTP error status.

  .then(response => {
    if(!response.ok) {
      if(response.status === 404) throw new Error("Not found")
      else if(response.status === 401) throw new Error("Unauthorized")
      else if(response.status === 418) throw new Error("I'm a teapot !")
      else throw new Error("Other error")
    else // ...
  .then(data => /* ... */)
  .catch(error => { /* ... */ })

Wretch throws when the response is not successful and contains helper methods to handle common codes.

  .notFound(error => { /* ... */ })
  .unauthorized(error => { /* ... */ })
  .error(418, error => { /* ... */ })
  .res(response => /* ... */)
  .catch(error => { /* uncaught errors */ })

Because sending a json object should be easy.

With fetch you have to set the header, the method and the body manually.

fetch("endpoint", {
  method: "POST",
  headers: { "Content-Type": "application/json" },
  body: JSON.stringify({ "hello": "world" })
}).then(response => /* ... */)
// Omitting the data retrieval and error management parts…

With wretch, you have shorthands at your disposal.

  .post({ "hello": "world" })
  .res(response => /* ... */)

Because configuration should not rhyme with repetition.

A Wretch object is immutable which means that you can reuse previous instances safely.

// Cross origin authenticated requests on an external API
const externalApi = wretch("http://external.api") // Base url
  // Authorization header
  .auth(`Bearer ${token}`)
  // Cors fetch options
  .options({ credentials: "include", mode: "cors" })
  // Handle 403 errors
  .resolve((_) => _.forbidden(handle403));

// Fetch a resource
const resource = await externalApi
  // Add a custom header for this request
  .headers({ "If-Unmodified-Since": "Wed, 21 Oct 2015 07:28:00 GMT" })

// Post a resource
  .post({ "Shiny new": "resource object" })


Package Manager

npm i wretch # or yarn/pnpm add wretch

<script> tag

The package contains multiple bundles depending on the format and feature set located under the /dist/bundle folder.

Bundle variants

💡 If you pick the core bundle, then to plug addons you must import them separately from /dist/bundle/addons/[addonName].min.js

Feature set File Name
Core features only wretch.min.js
Core + all addons wretch.all.min.js
Format Extension
ESM .min.mjs
CommonJS .min.cjs
UMD .min.js
  Pick your favourite CDN:
    - …

<!-- UMD import as window.wretch -->
<script src=""></script>

<!-- Modern import -->
<script type="module">
  import wretch from ''

  // ... //



wretch@^2 is compatible with modern browsers only. For older browsers please use wretch@^1.


Wretch is compatible with and tested in Node.js >= 14. Older versions of node may work but it is not guaranteed.

🥳 Starting from Node.js 18, node includes experimental fetch support. Wretch will work without installing any polyfill.

For older versions of Node.js, Wretch requires installing FormData and fetch polyfills.


Since the Node.js standard library does not provide a native implementation of fetch (and other Browsers-only APIs), polyfilling is mandatory.

The non-global way (preferred):

// w is a reusable wretch instance
const w = wretch().polyfills({
  fetch: require("node-fetch"),
  FormData: require("form-data"),
  URLSearchParams: require("url").URLSearchParams,


// Either mutate the global object…
global.fetch = require("node-fetch");
global.FormData = require("form-data");
global.URLSearchParams = require("url").URLSearchParams;

// …or use the static wretch.polyfills method to impact every wretch instance created afterwards.
  fetch: require("node-fetch"),
  FormData: require("form-data"),
  URLSearchParams: require("url").URLSearchParams,


Works with Deno >= 0.41.0 out of the box.

Types should be imported from /dist/types.d.ts.

// You can import wretch from any CDN that serve ESModules.
import wretch from "";

const text = await wretch("").get("/200").text();
console.log(text); // -> 200 OK



// ECMAScript modules
import wretch from "wretch"
// CommonJS
const wretch = require("wretch")
// Global variable (script tag)

Minimal Example

import wretch from "wretch"

// Instantiate and configure wretch
const api =
  wretch("", { mode: "cors" })
    .resolve(r => r.json())

try {
  // Fetch users
  const users = await api.get("/users")
  // Find all posts from a given user
  const user = users.find(({ name }) => name === "Nicholas Runolfsdottir V")
  const postsByUser = await api.get(`/posts?userId=${}`)
  // Create a new post
  const newPost = await api.url("/posts").post({
    title: "New Post",
    body: "My shiny new post"
  // Patch it
  await api.url("/posts/" +{
    title: "Updated Post",
    body: "Edited body"
  // Fetch it
  await api.get("/posts/" +
} catch (error) {
  // The API could return an empty object - in which case the status text is logged instead.
  const message =
    typeof error.message === "object" && Object.keys(error.message).length > 0
      ? JSON.stringify(error.message)
      : error.response.statusText
  console.error(`${error.status}: ${message}`)


A high level overview of the successive steps that can be chained to perform a request and parse the result.

// First, instantiate wretch
wretch(baseUrl, baseOptions)

The "request" chain starts here.

  // Optional - A set of helper methods to set the default options, set accept header, change the current url…
  .<helper method(s)>()
  // Optional - Serialize an object to json or FormData formats and sets the body & header field if needed
  .<body type>()
    // Required - Sends the get/put/post/delete/patch request.
  .<http method>()

The "response" chain starts here.

Fetch is called after the request chain ends and before the response chain starts.
The request is on the fly and now it is time to chain catchers and finally call a response type handler.

  // Optional - You can chain error handlers here
  // Required - Specify the data type you need, which will be parsed and handed to you
  .<response type>()
  // >> Ends the response chain.

From this point on, wretch returns a standard Promise.



💡 The API documentation is now autogenerated and hosted separately, click the links access it.

Static Methods 🔗

These methods are available from the main default export and can be used to instantiate wretch and configure it globally.

import wretch from "wretch"

wretch.options({ mode: "cors" })

let w = wretch("", { cache: "default" })

Helper Methods 🔗

Helper Methods are used to configure the request and program actions.

w = w
  .headers({ "Cache-Control": no-cache })

Body Types 🔗

Specify a body type if uploading data. Can also be added through the HTTP Method argument.

w = w.body("<html><body><div/></body></html>")

HTTP Methods 🔗

Sets the HTTP method and sends the request.

Calling an HTTP method ends the request chain and returns a response chain. You can pass optional url and body arguments to these methods.

// These shorthands:
wretch().post({ json: "body" }, "/url");
// Are equivalent to:
wretch().json({ json: "body" }).url("/url").post();

NOTE: if the body argument is an Object it is assumed that it is a JSON payload and it will have the same behaviour as calling .json(body) unless the Content-Type header has been set to something else beforehand.

Catchers 🔗

Catchers are optional, but if none are provided an error will still be thrown for http error codes and it will be up to you to catch it.

  .badRequest((err) => console.log(err.status))
  .unauthorized((err) => console.log(err.status))
  .forbidden((err) => console.log(err.status))
  .notFound((err) => console.log(err.status))
  .timeout((err) => console.log(err.status))
  .internalError((err) => console.log(err.status))
  .error(418, (err) => console.log(err.status))
  .fetchError((err) => console.log(err))

The error passed to catchers is enhanced with additional properties.

type WretchError = Error & {
  status: number;
  response: WretchResponse;
  text?: string;
  json?: Object;

The original request is passed along the error and can be used in order to perform an additional request.

  .unauthorized(async (error, req) => {
    // Renew credentials
    const token = await wretch("/renewtoken").get().text();
    // Replay the original request with new credentials
    return req.auth(token).get().unauthorized((err) => {
      throw err;
  // The promise chain is preserved as expected
  // ".then" will be performed on the result of the original request
  // or the replayed one (if a 401 error was thrown)

Response Types 🔗

Setting the final response body type ends the chain and returns a regular promise.

All these methods accept an optional callback, and will return a Promise resolved with either the return value of the provided callback or the expected type.

// Without a callback
wretch("...").get().json().then(json => /* json is the parsed json of the response body */)
// Without a callback using await
const json = await wretch("...").get().json()
// With a callback the value returned is passed to the Promise
wretch("...").get().json(json => "Hello world!").then(console.log) // => Hello world!

If an error is caught by catchers, the response type handler will not be called.


Addons are separate pieces of code that you can import and plug into wretch to add new features.

import FormDataAddon from "wretch/addons/formData"
import QueryStringAddon from "wretch/addons/queryString"

// Add both addons
const w = wretch().addon(FormDataAddon).addon(QueryStringAddon)

// Additional features are now available
w.formData({ hello: "world" }).query({ check: true })

Typescript should also be fully supported and will provide completions.

QueryString 🔗

Used to construct and append the query string part of the URL from an object.

import QueryStringAddon from "wretch/addons/queryString"

let w = wretch("").addon(QueryStringAddon);
// url is
w = w.query({ a: 1, b: 2 });
// url is now
w = w.query({ c: 3, d: [4, 5] });
// url is now
w = w.query("five&six&seven=eight");
// url is now
w = w.query({ reset: true }, true);
// url is now

FormData 🔗

Adds a helper method to serialize a multipart/form-data body from an object.

import FormDataAddon from "wretch/addons/formData"

const form = {
  duck: "Muscovy",
  duckProperties: {
    beak: {
      color: "yellow",
    legs: 2,
  ignored: {
    key: 0,

// Will append the following keys to the FormData payload:
// "duck", "duckProperties[beak][color]", "duckProperties[legs]"
wretch("...").addons(FormDataAddon).formData(form, ["ignored"]).post();

FormUrl 🔗

Adds a method to serialize a application/x-www-form-urlencoded body from an object.

import FormUrlAddon from "wretch/addons/formUrl"

const form = { a: 1, b: { c: 2 } };
const alreadyEncodedForm = "a=1&b=%7B%22c%22%3A2%7D";

// Automatically sets the content-type header to "application/x-www-form-urlencoded"

Abort 🔗

Adds the ability to abort requests and set timeouts using AbortController and signals under the hood.

import AbortAddon from "wretch/addons/abort"

Only compatible with browsers that support AbortControllers. Otherwise, you could use a (partial) polyfill.

Use cases :

const [c, w] = wretch("...")
  .onAbort((_) => console.log("Aborted !"))

w.text((_) => console.log("should never be called"));

// Or :

const controller = new AbortController();

  .onAbort((_) => console.log("Aborted !"))
  .text((_) => console.log("should never be called"));

// 1 second timeout
wretch("...").addon(AbortAddon()).get().setTimeout(1000).json(_ =>
  // will not be called if the request timeouts

Progress 🔗

Adds the ability to monitor progress when downloading a response.

Compatible with all platforms implementing the TransformStream WebAPI.

import ProgressAddon from "wretch/addons/progress"

  // Called with the number of bytes loaded and the total number of bytes to load
  .progress((loaded, total) => {
    console.log(`${(loaded / total * 100).toFixed(0)}%`)

Performance 🔗

Adds the ability to measure requests using the Performance Timings API.

Uses the Performance API (browsers & Node.js) to expose timings related to the underlying request.

💡 Make sure to follow the additional instructions in the documentation to setup Node.js if necessary.


Middlewares are functions that can intercept requests before being processed by Fetch. Wretch includes a helper to help replicate the middleware style.

import wretch from "wretch"
import { retry, dedupe } from "wretch/middlewares"

const w = wretch().middlewares([retry(), dedupe()])

💡 The following middlewares were previously provided by the wretch-middlewares package.

Retry 🔗

Retries a request multiple times in case of an error (or until a custom condition is true).

import wretch from 'wretch'
import { retry } from 'wretch/middlewares'

    /* Options - defaults below */
    delayTimer: 500,
    delayRamp: (delay, nbOfAttempts) => delay * nbOfAttempts,
    maxAttempts: 10,
    until: (response, error) => response && response.ok,
    onRetry: null,
    retryOnNetworkError: false,
    resolveWithLatestResponse: false
])./* ... */

// You can also return a Promise, which is useful if you want to inspect the body:
    until: response =>
      response.clone().json().then(body =>
        body.field === 'something'

Dedupe 🔗

Prevents having multiple identical requests on the fly at the same time.

import wretch from 'wretch'
import { dedupe } from 'wretch/middlewares'

    /* Options - defaults below */
    skip: (url, opts) => opts.skipDedupe || opts.method !== 'GET',
    key: (url, opts) => opts.method + '@' + url,
    resolver: response => response.clone()
])./* ... */

Throttling Cache 🔗

A throttling cache which stores and serves server responses for a certain amount of time.

import wretch from 'wretch'
import { throttlingCache } from 'wretch/middlewares'

    /* Options - defaults below */
    throttle: 1000,
    skip: (url, opts) => opts.skipCache || opts.method !== 'GET',
    key: (url, opts) => opts.method + '@' + url,
    clear: (url, opts) => false,
    invalidate: (url, opts) => null,
    condition: response => response.ok,
    flagResponseOnCacheHit: '__cached'
])./* ... */

Delay 🔗

Delays the request by a specific amount of time.

import wretch from 'wretch'
import { delay } from 'wretch/middlewares'

])./* ... */

Writing a Middleware

Basically a Middleware is a function having the following signature :

// A middleware accepts options and returns a configured version
type Middleware = (options?: { [key: string]: any }) => ConfiguredMiddleware;
// A configured middleware (with options curried)
type ConfiguredMiddleware = (next: FetchLike) => FetchLike;
// A "fetch like" function, accepting an url and fetch options and returning a response promise
type FetchLike = (
  url: string,
  opts: WretchOptions,
) => Promise<WretchResponse>;


If you need to manipulate data within your middleware and expose it for later consumption, a solution could be to pass a named property to the wretch options (suggested name: context).

Your middleware can then take advantage of that by mutating the object reference.

const contextMiddleware = (next) =>
  (url, opts) => {
    if (opts.context) {
      // Mutate "context" = "anything";
    return next(url, opts);

// Provide the reference to a "context" object
const context = {};
const res = await wretch("...")
  // Pass "context" by reference as an option
  .options({ context })

console.log(; // prints "anything"

Advanced examples

 👀 Show me the code
/* A simple delay middleware. */
const delayMiddleware = delay => next => (url, opts) => {
  return new Promise(res => setTimeout(() => res(next(url, opts)), delay))

/* Returns the url and method without performing an actual request. */
const shortCircuitMiddleware = () => next => (url, opts) => {
  // We create a new Response object to comply because wretch expects that from fetch.
  const response = new Response()
  response.text = () => Promise.resolve(opts.method + "@" + url)
  response.json = () => Promise.resolve({ url, method: opts.method })
  // Instead of calling next(), returning a Response Promise bypasses the rest of the chain.
  return Promise.resolve(response)

/* Logs all requests passing through. */
const logMiddleware = () => next => (url, opts) => {
  console.log(opts.method + "@" + url)
  return next(url, opts)

/* A throttling cache. */
const cacheMiddleware = (throttle = 0) => {

  const cache = new Map()
  const inflight = new Map()
  const throttling = new Set()

  return next => (url, opts) => {
    const key = opts.method + "@" + url

    if(!opts.noCache && throttling.has(key)) {
      // If the cache contains a previous response and we are throttling, serve it and bypass the chain.
        return Promise.resolve(cache.get(key).clone())
      // If the request in already in-flight, wait until it is resolved
      else if(inflight.has(key)) {
        return new Promise((resolve, reject) => {
          inflight.get(key).push([resolve, reject])

    // Init. the pending promises Map
      inflight.set(key, [])

    // If we are not throttling, activate the throttle for X milliseconds
    if(throttle && !throttling.has(key)) {
      setTimeout(() => { throttling.delete(key) }, throttle)

    // We call the next middleware in the chain.
    return next(url, opts)
      .then(_ => {
        // Add a cloned response to the cache
        cache.set(key, _.clone())
        // Resolve pending promises
        inflight.get(key).forEach((([resolve, reject]) => resolve(_.clone()))
        // Remove the inflight pending promises
        // Return the original response
        return _
      .catch(_ => {
        // Reject pending promises on error
        inflight.get(key).forEach(([resolve, reject]) => reject(_))
        throw _

// To call a single middleware
const cache = cacheMiddleware(1000)

// To chain middlewares
}).get().text(_ => console.log(text))

// To test the cache middleware more thoroughly
const wretchCache = wretch().middlewares([cacheMiddleware(1000)])
const printResource = (url, timeout = 0) =>
  setTimeout(_ => wretchCache.url(url).get().notFound(console.error).text(console.log), timeout)
// The resource url, change it to an invalid route to check the error handling
const resourceUrl = "/"
// Only two actual requests are made here even though there are 30 calls
for(let i = 0; i < 10; i++) {
  printResource(resourceUrl, 500)
  printResource(resourceUrl, 1500)


Cloudflare Workers

It seems like using wretch in a Cloudflare Worker environment is not possible out of the box, as the Cloudflare Response implementation does not implement the type property and throws an error when trying to access it.

Please check the issue #159 for more information.


The following middleware should fix the issue (thanks @jimmed 🙇):

  (next) => async (url, opts) => {
    const response = await next(url, opts);
    try {
      Reflect.get(response, "type", response);
    } catch (error) {
      Object.defineProperty(response, "type", {
        get: () => "default",
    return response;

Headers Case Sensitivity

The Request object from the Fetch API uses the Headers class to store headers under the hood. This class is case-insensitive, meaning that setting both will actually appends the value to the same key:

const headers = new Headers();
headers.append("Accept", "application/json");
headers.append("accept", "application/json");
headers.forEach((value, key) => console.log(key, value));
// prints: accept application/json, application/json

When using wretch, please be mindful of this limitation and avoid setting the same header multiple times with a different case:

  .headers("content-type": "application/json")
  // .json is a shortcut for .headers("Content-Type": "application/json").post().json()
  .json({ foo: "bar" })
  // Wretch stores the headers inside a plain javascript object and will not deduplicate them.
  // Later on when fetch builds the Headers object the content type header will be set twice
  // and its value will be "application/json, application/json".
  // Ultimately this is certainly not what you want.

Please check the issue #80 for more information.


You can use the following middleware to deduplicate headers (thanks @jimmed 🙇):

export const manipulateHeaders =
  callback => next => (url, { headers, ...opts }) => {
    const nextHeaders = callback(new Headers(headers))
    return next(url, { ...opts, headers: nextHeaders })

export const dedupeHeaders = (dedupeHeaderLogic = {}) => {
  const deduperMap = new Map(
    Object.entries(dedupeHeaderLogic).map(([k, v]) => [k.toLowerCase(), v]),
  const dedupe = key =>
    deduperMap.get(key.toLowerCase()) ?? (values => new Set(values))

  return manipulateHeaders((headers) => {
    Object.entries(headers.raw()).forEach(([key, values]) => {
      const deduped = Array.from(dedupe(key)(values))
      deduped.forEach((value, index) =>
        headers[index ? 'append' : 'set'](key.toLowerCase(), value),
    return headers

// By default, it will deduplicate identical values for a given header. This can be used as follows:
// If there is a specific header for which the defaults cause problems, then you can provide a callback to handle deduplication yourself:
    Accept: (values) => values.filter(v => v !== '*/*')

Migration from v1


Wretch has been completely rewritten with the following goals in mind:

  • reduce its size by making it modular
  • preserve the typescript type coverage
  • improve the API by removing several awkward choices


wretch@1 was transpiled to es5, wretch@2 is now transpiled to es2018. Any "modern" browser and Node.js versions >= 14 should parse the library without issues.

If you need compatibility with older browsers/nodejs versions then either stick with v1, use poyfills or configure @babel to make it transpile wretch.


Some features that were part of wretch v1 are now split apart and must be imported through addons. It is now needed to pass the Addon to the .addon method to register it.

Please refer to the Addons documentation.

/* Previously (wretch@1) */
import wretch from "wretch"

wretch.formData({ hello: "world" }).query({ check: true })

/* Now (wretch@2) */
import FormDataAddon from "wretch/addons/formData"
import QueryStringAddon from "wretch/addons/queryString"
import wretch as baseWretch from "wretch"

// Add both addons
const wretch = baseWretch().addon(FormDataAddon).addon(QueryStringAddon)

// Additional features are now available
wretch.formData({ hello: "world" }).query({ check: true })


Types have been renamed and refactored, please update your imports accordingly and refer to the typescript api documentation.

API Changes

Replace / Mixin arguments

Some functions used to have a mixin = true argument that could be used to merge the value, others a replace = false argument performing the opposite. In v2 there are only replace = false arguments but the default behaviour should be preserved.

/* Previously (wretch@1) */
wretch.options({ credentials: "same-origin" }, false) // false: do not merge the value
wretch.options({ credentials: "same-origin" }) // Default behaviour stays the same

/* Now (wretch@2) */
wretch.options({ credentials: "same-origin" }, true) // true: replace the existing value
wretch.options({ credentials: "same-origin" }) // Default behaviour stays the same

HTTP methods extra argument

In v1 it was possible to set fetch options while calling the http methods to end the request chain.

/* Previously (wretch@1) */
wretch("...").get({ my: "option" })

This was a rarely used feature and the extra argument now appends a string to the base url.

/* Now (wretch@2) */

Replay function

The .replay function has been renamed to .fetch.