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.
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 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.
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:
- 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 aHeaders
object or an object literal withByteString
values.body
: Any body that you want to add to your request: this can be aBlob
,BufferSource
,FormData
,URLSearchParams
, orUSVString
object. Note that a request using theGET
orHEAD
method cannot have a body.mode
: The mode you want to use for the request, e.g.,cors
,no-cors
, orsame-origin.
credentials
: The request credentials you want to use for the request:omit
,same-origin
, orinclude
. To automatically send cookies for the current domain, this option must be provided. Starting with Chrome 50, this property also takes aFederatedCredential
instance or aPasswordCredential
instance.cache
: The cache mode you want to use for the request:default
,no-store
,reload
,no-cache
,force-cache
, oronly-if-cached
.redirect
: The redirect mode to use:follow
(automatically follow redirects),error
(abort with an error if a redirect occurs), ormanual
(handle redirects manually). In Chrome the default wasfollow
before Chrome 47 andmanual
starting with Chrome 47.referrer
: AUSVString
specifyingno-referrer
,client
, or a URL. The default isclient
.referrerPolicy
: Specifies the value of the referer HTTP header. May be one ofno-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=
).signal
: AFetchSignal
object instance; allows you to communicate with a fetch request and control it via aFetchController
.observe
: AnObserverCallback
object — this object's sole purpose is to provide a callback function that runs when the fetch request runs. This returns aFetchObserver
object that can be used to retrieve information concerning the status of a fetch request.
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 | 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 | Editor's Draft | Adds FederatedCredential or PasswordCredential instance as a possible value for init.credentials . |
Browser compatibility
Feature | Chrome | Edge | Firefox (Gecko) | Internet Explorer | Opera | Safari (WebKit) |
---|---|---|---|---|---|---|
Basic support | 42 | 14 | 34 (34)[1] 39 (39) 52 (52)[2] |
No support | 29 28[1] |
No support |
Streaming response body | 43 | 14 | ? | ? | ? | ? |
Support for blob: and data: |
48 | No support | ? | ? | ? | ? |
referrerPolicy |
52 | ? | ? | ? | 39 | ? |
signal and observer |
No support | No support | No support[3] | No support | No support | No support |
Feature | Android | Android Webview | Edge | Firefox Mobile (Gecko) | IE Phone | Opera Mobile | Safari Mobile | Chrome for Android |
---|---|---|---|---|---|---|---|---|
Basic support | No support | 42 | 14 | 52.0 (52)[2] | No support | No support | No support | 42 |
Streaming response body | No support | 43 | 14 | ? | ? | ? | ? | 43 |
Support for blob: and data: |
No support | 43 | No support | ? | ? | ? | ? | 43 |
referrerPolicy |
No support | 52 | ? | ? | ? | 39 | ? | 52 |
signal and observer |
No support | No support | No support | No support[3] | No support | No support | No support | No support |
[1] API is implemented behind a preference.
[2] fetch()
now defined on WindowOrWorkerGlobalScope
mixin.
[3] Hidden behind a preference in 55+ Nightly. In about:config, you need to create two new boolean prefs — dom.fetchObserver.enabled
and dom.fetchController.enabled
— and set the values of both to true
.