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This is an experimental technology
Because this technology's specification has not stabilized, check the compatibility table for usage in various browsers. Also note that the syntax and behavior of an experimental technology is subject to change in future versions of browsers as the specification changes.

The fetch() method of the GlobalFetch mixin starts the process of fetching a resource. This returns a promise that resolves to the Response object representing the response to your request.

GlobalFetch 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 rejects with a TypeError when a network error is encountered, although this usually means a permissions issue or similar. An accurate check for a successful fetch() would include checking that the promise resolved, then checking that the Response.ok property has a value of true. An HTTP status of 404 does not constitute a network error.

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

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: default, no-store, reload, no-cache, force-cache, or only-if-cached.
  • 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 was follow before Chrome 47 and manual starting with Chrome 47.
  • referrer: A USVString specifying no-referrerclient, 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=).

Return value

A Promise that resolves to a Response object.

Exceptions

Type Description
TypeError Since Firefox 43, fetch() will throw a TypeError if the URL has credentials, such as http://user:password@example.com.

Example

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.

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

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

fetch(myRequest).then(function(response) {
  return response.blob();
}).then(function(response) {
  var 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():

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

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

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

var 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.:

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

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

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

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

Specifications

Specification Status Comment
Fetch
The definition of 'fetch()' in that specification.
Living Standard Initial definition
Credential Management Level 1 Editor's Draft Adds FederatedCredential or PasswordCredential instance as a possible value for init.credentials.

Browser compatibility

Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari (WebKit)
Basic support 42.0 39 (39)
34[1]
No support 29
28[1]
No support
Streaming response body 43.0 ? ? ? ?
Support for blob: and data: 48.0        
referrerPolicy 52.0     39  
Feature Android Android Webview Firefox Mobile (Gecko) Firefox OS (Gecko) IE Phone Opera Mobile Safari Mobile Chrome for Android
Basic support No support 42.0 No support No support No support No support No support 42.0
Streaming response body No support 43.0 ? ? ? ? ? 43.0
Support for blob: and data: No support 43.0           43.0
referrerPolicy No support 52.0       39   52.0

[1] This API is implemented behind a preference.

See also

Document Tags and Contributors

 Last updated by: jpmedley,