Web/API/WindowOrWorkerGlobalScope/fetch

The fetch() method of the WindowOrWorkerGlobalScope mixin starts the process of fetching a resource from the network, returning a promise which is fulfilled once the response is available. The promise resolves to the Response object representing the response to your request. The promise does not reject on HTTP errors — it only rejects on network errors. You must use then handlers to check for HTTP errors.

WindowOrWorkerGlobalScope is implemented by both Window and WorkerGlobalScope, which means that the fetch() method is available in pretty much any context in which you might want to fetch resources.

A fetch() promise only rejects when a network error is encountered (which is usually when there’s a permissions issue or similar). A fetch() promise does not reject on HTTP errors (404, etc.). Instead, a then() handler must check the Response.ok and/or Response.status properties.

The fetch() method is controlled by the connect-src directive of Content Security Policy rather than the directive of the resources it's retrieving.

Note: The fetch() method's parameters are identical to those of the Request() constructor.

Syntax

const fetchResponsePromise = fetch(resource [, init])

Parameters

resource: This defines the resource that you wish to fetch. This can either be:

A USVString containing the direct URL of the resource you want to fetch. Some browsers accept the blob: and data: schemes. A Request object.

init Optional: An object containing any custom settings that you want to apply to the request. The possible options are:

method The request method, e.g., GET, POST. Note that the Origin header is not set on Fetch requests with a method of HEAD or GET. (This behavior was corrected in Firefox 65 — see bug 1508661). headers Any headers you want to add to your request, contained within a Headers object or an object literal with ByteString values. Note that some names are forbidden. body Any body that you want to add to your request: this can be a Blob, BufferSource, FormData, URLSearchParams, USVString, or ReadableStream object. Note that a request using the GET or HEAD method cannot have a body. mode The mode you want to use for the request, e.g., cors, no-cors, or same-origin. credentials The request credentials you want to use for the request: omit, same-origin, or include. To automatically send cookies for the current domain, this option must be provided. Starting with Chrome 50, this property also takes a FederatedCredential instance or a PasswordCredential instance. cache The cache mode you want to use for the request. redirect The redirect mode to use: follow (automatically follow redirects), error (abort with an error if a redirect occurs), or manual (handle redirects manually). In Chrome the default is follow (before Chrome 47 it defaulted to manual). referrer A USVString specifying the referrer of the request. This can be a same-origin URL, about:client, or an empty string. referrerPolicy Specifies the referrer policy to use for the request. May be one of no-referrer, no-referrer-when-downgrade, same-origin, origin, strict-origin, origin-when-cross-origin, strict-origin-when-cross-origin, or unsafe-url. integrity Contains the subresource integrity value of the request (e.g., sha256-BpfBw7ivV8q2jLiT13fxDYAe2tJllusRSZ273h2nFSE=). keepalive The keepalive option can be used to allow the request to outlive the page. Fetch with the keepalive flag is a replacement for the Navigator.sendBeacon() API. signal An AbortSignal object instance; allows you to communicate with a fetch request and abort it if desired via an AbortController.

Return value

A Promise that resolves to a Response object.

Exceptions

AbortError: The request was aborted due to a call to the AbortController method abort() method.
TypeError: The specified URL string includes user credentials. This information should instead be provided using an Authorization header.

Examples

In our Fetch Request example (see [[../../../../../../../mdn.github.io/fetch-examples/fetch-request/index|Fetch Request live]]) we create a new Request object using the relevant constructor, then fetch it using a fetch() call. Since we are fetching an image, we run Body.blob() on the response to give it the proper MIME type so it will be handled properly, then create an Object URL of it and display it in an <img> element.

const myImage = document.querySelector('img');

let myRequest = new Request('flowers.jpg');

fetch(myRequest)
.then(function(response) {
  if (!response.ok) {
    throw new Error(`HTTP error! status: ${response.status}`);
  }
  return response.blob();
})
.then(function(response) {
  let objectURL = URL.createObjectURL(response);
  myImage.src = objectURL;
});

In the Fetch with init then Request example (see [[../../../../../../../mdn.github.io/fetch-examples/fetch-with-init-then-request/index|Fetch Request init live]]), we do the same thing except that we pass in an init object when we invoke fetch():

const myImage = document.querySelector('img');

let myHeaders = new Headers();
myHeaders.append('Content-Type', 'image/jpeg');

const myInit = {
  method: 'GET',
  headers: myHeaders,
  mode: 'cors',
  cache: 'default'
};

let myRequest = new Request('flowers.jpg');

fetch(myRequest, myInit).then(function(response) {
  // ... 
});

You could also pass the init object in with the Request constructor to get the same effect:

let myRequest = new Request('flowers.jpg', myInit);

You can also use an object literal as headers in init.

const myInit = {
  method: 'GET',
  headers: {
    'Content-Type': 'image/jpeg'
  },
  mode: 'cors',
  cache: 'default'
};

let myRequest = new Request('flowers.jpg', myInit);

Specifications

Specification	Status	Comment
FetchThe definition of 'fetch()' in that specification.	Living Standard	Defined in a `WindowOrWorkerGlobalScope` partial in the newest spec.
FetchThe definition of 'fetch()' in that specification.	Living Standard	Initial definition
Credential Management Level 1	Working Draft	Adds `FederatedCredential` or `PasswordCredential` instance as a possible value for `init.credentials`.

Browser compatibility

Update compatibility data on GitHub

	Desktop						Mobile
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	Android webview	Chrome for Android	Firefox for Android	Opera for Android	Safari on iOS	Samsung Internet
`fetch` Experimental'	Chrome Full support 42	Edge Full support 14	Firefox Full support 39 Full support 39 Full support 34 Disabled' Disabled' From version 34: this feature is behind the `dom.fetch.enable` preference. To change preferences in Firefox, visit about:config. Full support 52 Notes' Notes' `fetch()` now defined on `WindowOrWorkerGlobalScope` mixin.	IE No support No	Opera Full support 29 Full support 29 Full support 28 Disabled' Disabled' From version 28: this feature is behind the `Experimental Web Platform Features` preference.	Safari Full support 10.1	WebView Android Full support 42	Chrome Android Full support 42	Firefox Android Full support 39 Full support 39 Full support 34 Disabled' Disabled' From version 34: this feature is behind the `dom.fetch.enable` preference. To change preferences in Firefox, visit about:config. Full support 52 Notes' Notes' `fetch()` now defined on `WindowOrWorkerGlobalScope` mixin.	Opera Android Full support 29 Full support 29 Full support 28 Disabled' Disabled' From version 28: this feature is behind the `Experimental Web Platform Features` preference.	Safari iOS Full support 10.3	Samsung Internet Android Full support 4.0
Support for blob: and data: Experimental'	Chrome Full support 48	Edge Full support 79	Firefox ?	IE No support No	Opera ?	Safari ?	WebView Android Full support 43	Chrome Android Full support 48	Firefox Android ?	Opera Android ?	Safari iOS ?	Samsung Internet Android Full support 5.0
referrerPolicy	Chrome Full support 52	Edge Full support 79	Firefox Full support 52	IE No support No	Opera Full support 39	Safari Full support 11.1	WebView Android Full support 52	Chrome Android Full support 52	Firefox Android Full support 52	Opera Android Full support 41	Safari iOS No support No	Samsung Internet Android Full support 6.0
signal Experimental'	Chrome Full support 66	Edge Full support 16	Firefox Full support 57	IE No support No	Opera Full support 53	Safari Full support 11.1	WebView Android Full support 66	Chrome Android Full support 66	Firefox Android Full support 57	Opera Android Full support 47	Safari iOS Full support 11.3	Samsung Internet Android Full support 9.0
Streaming response body Experimental'	Chrome Full support 43	Edge Full support 14	Firefox Full support Yes Disabled' Full support Yes Disabled' Disabled' This feature is behind the `dom.streams.enabled` preference and the `javascript.options.streams` preference. To change preferences in Firefox, visit about:config.	IE No support No	Opera Full support 29	Safari Full support 10.1	WebView Android Full support 43	Chrome Android Full support 43	Firefox Android No support No	Opera Android No support No	Safari iOS Full support 10.3	Samsung Internet Android Full support 4.0

Legend

Full support: Full support
No support: No support
Compatibility unknown: Compatibility unknown
Experimental. Expect behavior to change in the future.': Experimental. Expect behavior to change in the future.
See implementation notes.': See implementation notes.
User must explicitly enable this feature.': User must explicitly enable this feature.