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.
Promise<Response> fetch(input[, init]);
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
.A Promise
that resolves to a Response
object.
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] . |
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);
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 . |
Desktop | ||||||
---|---|---|---|---|---|---|
Chrome | Edge | Firefox | Internet Explorer | Opera | Safari | |
Basic support | 42 | 14 | 39
|
No | 29
|
10 |
Streaming response body | 43 | 14 | Yes
|
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
|
? | 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 |
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Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.
https://developer.mozilla.org/en-US/docs/Web/API/WindowOrWorkerGlobalScope/fetch