W3cubDocs

/DOM

WindowOrWorkerGlobalScope.fetch

The fetch() method of the WindowOrWorkerGlobalScope mixin starts the process of fetching a resource from the network. This returns a promise that resolves to the Response object representing the response to your request. The promise does not reject on HTTP errors — instead it only rejects only network errors; then handlers must check for HTTP errors.

WorkerOrGlobalScope 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

Promise<Response> fetch(input[, init]);

Parameters

input
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 blob: and data: as schemes.
  • A Request object.
init Optional
An options 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.
  • headers: Any headers you want to add to your request, contained within a Headers object or an object literal with ByteString values.
  • body: Any body that you want to add to your request: this can be a Blob, BufferSource, FormData, URLSearchParams, or USVString 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 no-referrer, client, or a URL. The default is client.
  • referrerPolicy: Specifies the value of the referer HTTP header. May be one of no-referrer, no-referrer-when-downgrade, origin, origin-when-cross-origin, 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

Type Description
AbortError The request was aborted (using AbortController.abort()).
TypeError Since Firefox 43, fetch() will throw a TypeError if the URL has credentials, such as http://user:[email protected].

Examples

In our Fetch Request example (see 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 our Fetch with init then Request example (see 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) {
  ... 
});

Note that you could also pass the init object in with the Request constructor to get the same effect, e.g.:

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
Fetch
The definition of 'fetch()' in that specification.
Living Standard Defined in a WindowOrWorkerGlobalScope partial in the newest spec.
Fetch
The 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 compatibilityUpdate compatibility data on GitHub

Desktop
Chrome Edge Firefox Internet Explorer Opera Safari
Basic support 42 14 39
39
34
Disabled
Disabled From version 34: this feature is behind the dom.fetch.enable preference. To change preferences in Firefox, visit about:config.
52
fetch() now defined on WindowOrWorkerGlobalScope mixin.
No 29
29
28
Disabled
Disabled From version 28: this feature is behind the Experimental Web Platform Features preference.
10
Streaming response body 43 14 Yes
Disabled
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.
No 29 10
Support for blob: and data: 48 No ? No ? ?
referrerPolicy 52 No 52 No 39 11.1
signal 66 16 57 No 53 11.1
Mobile
Android webview Chrome for Android Edge Mobile Firefox for Android Opera for Android iOS Safari Samsung Internet
Basic support 42 42 14 39
39
34
Disabled
Disabled From version 34: this feature is behind the dom.fetch.enable preference. To change preferences in Firefox, visit about:config.
52
fetch() now defined on WindowOrWorkerGlobalScope mixin.
? 10 ?
Streaming response body 43 43 14 No No 10 ?
Support for blob: and data: 43 43 No ? ? ? ?
referrerPolicy 52 52 No 52 39 No ?
signal 66 66 16 57 53 11.1 No

See also

© 2005–2018 Mozilla Developer Network and individual contributors.
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.
https://developer.mozilla.org/en-US/docs/Web/API/WindowOrWorkerGlobalScope/fetch