Request: Request() constructor
The Request()
constructor creates a new
Request
object.
Syntax
js
new Request(input)
new Request(input, options)
Parameters
input
-
Defines the resource that you wish to fetch. This can either be:
- A string containing the URL of the resource you want to fetch. The URL may be relative to the base URL, which is the document's
baseURI
in a window context, orWorkerGlobalScope.location
in a worker context. -
A
Request
object, effectively creating a copy. Note the following behavioral updates to retain security while making the constructor less likely to throw exceptions:-
If this object exists on another origin to the constructor call, the
Request.referrer
is stripped out. -
If this object has a
Request.mode
ofnavigate
, themode
value is converted tosame-origin
.
-
If this object exists on another origin to the constructor call, the
- A string containing the URL of the resource you want to fetch. The URL may be relative to the base URL, which is the document's
options
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
. The default isGET
. headers
-
Any headers you want to add to your request, contained within a
Headers
object or an object literal withString
values. body
-
Any body that you want to add to your request: this can be a
Blob
, anArrayBuffer
, aTypedArray
, aDataView
, aFormData
, aURLSearchParams
, a string, or aReadableStream
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
,same-origin
, ornavigate
. The default iscors
. credentials
-
The request credentials you want to use for the request:
omit
,same-origin
, orinclude
. The default issame-origin
. cache
-
The cache mode you want to use for the request.
redirect
-
The redirect mode to use:
follow
,error
, ormanual
. The default isfollow
. referrer
-
A string specifying
no-referrer
,client
, or a URL. The default isabout:client
. referrerPolicy
-
A string that changes how the referrer header is populated during certain actions (e.g., fetching subresources, prefetching, performing navigations).
integrity
-
Contains the subresource integrity value of the request (e.g.,
sha256-BpfBw7ivV8q2jLiT13fxDYAe2tJllusRSZ273h2nFSE=
). keepalive
-
A boolean that indicates whether to make a persistent connection for multiple requests/responses.
signal
-
An AbortSignal object which can be used to communicate with/abort a request.
priority
-
Specifies the priority of the fetch request relative to other requests of the same type. Must be one of the following strings:
high
: A high priority fetch request relative to other requests of the same type.low
: A low priority fetch request relative to other requests of the same type.auto
: Automatically determine the priority of the fetch request relative to other requests of the same type (default).
If you construct a new
Request
from an existingRequest
, any options you set in an options argument for the new request replace any corresponding options set in the originalRequest
. For example:js
const oldRequest = new Request( "https://github.com/mdn/content/issues/12959", { headers: { From: "webmaster@example.org" } }, ); oldRequest.headers.get("From"); // "webmaster@example.org" const newRequest = new Request(oldRequest, { headers: { From: "developer@example.org" }, }); newRequest.headers.get("From"); // "developer@example.org"
Errors
Type | Description |
---|---|
TypeError |
Since Firefox 43,
Request() will throw a TypeError if the URL has
credentials, such as http://user:password@example.com.
|
Examples
In our Fetch Request example (see Fetch Request live) we
create a new Request
object using the constructor, then fetch it using a
fetch()
call. Since we are fetching an image, we run
Response.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.
js
const myImage = document.querySelector("img");
const myRequest = new Request("flowers.jpg");
fetch(myRequest)
.then((response) => response.blob())
.then((response) => {
const objectURL = URL.createObjectURL(response);
myImage.src = objectURL;
});
In our Fetch Request with init example (see Fetch Request init live) we do the same thing except that we pass in an options object when we
invoke fetch()
:
js
const myImage = document.querySelector("img");
const myHeaders = new Headers();
myHeaders.append("Content-Type", "image/jpeg");
const myOptions = {
method: "GET",
headers: myHeaders,
mode: "cors",
cache: "default",
};
const myRequest = new Request("flowers.jpg", myOptions);
fetch(myRequest).then((response) => {
// ...
});
Note that you could also pass myOptions
into the fetch
call to get
the same effect, e.g.:
js
fetch(myRequest, myOptions).then((response) => {
// ...
});
You can also use an object literal as headers
in myOptions
.
js
const myOptions = {
method: "GET",
headers: {
"Content-Type": "image/jpeg",
},
mode: "cors",
cache: "default",
};
const myRequest = new Request("flowers.jpg", myOptions);
You may also pass a Request
object to the Request()
constructor to create a copy of the Request (This is similar to calling the
clone()
method.)
js
const copy = new Request(myRequest);
Note: This last usage is probably only useful in ServiceWorkers.
Specifications
Specification |
---|
Fetch Standard # ref-for-dom-request① |
Browser compatibility
BCD tables only load in the browser