Request: Request() constructor

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, or WorkerGlobalScope.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 of navigate, the mode value is converted to same-origin.

options Optional

An object containing any custom settings that you want to apply to the request. The possible options are:

body

Any body that you want to add to your request: this can be a Blob, an ArrayBuffer, a TypedArray, a DataView, a FormData, a URLSearchParams, a string, or a ReadableStream object. Note that a request using the GET or HEAD method cannot have a body.

browsingTopics Experimental

A boolean specifying that the selected topics for the current user should be sent in a Sec-Browsing-Topics header with the associated request. See Using the Topics API for more details.

cache

The cache mode you want to use for the request.

credentials

The request credentials you want to use for the request: omit, same-origin, or include. The default is same-origin.

headers

Any headers you want to add to your request, contained within a Headers object or an object literal with String values.

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.

method

The request method, e.g., GET, POST. The default is GET.

mode

The mode you want to use for the request, e.g., cors, no-cors, same-origin, or navigate. The default is cors.

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).

redirect

The redirect mode to use: follow, error, or manual. The default is follow.

referrer

A string specifying no-referrer, client, or a URL. The default is about:client.

referrerPolicy

A string that changes how the referrer header is populated during certain actions (e.g., fetching subresources, prefetching, performing navigations).

signal

An AbortSignal object which can be used to communicate with/abort a request.

If you construct a new Request from an existing Request, any options you set in an options argument for the new request replace any corresponding options set in the original Request. 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"

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.

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(). In this case, we can set a Cache-Control value to indicate what kind of cached responses we're okay with:

const myImage = document.querySelector("img");
const reqHeaders = new Headers();

// A cached response is okay unless it's more than a week old.
reqHeaders.set("Cache-Control", "max-age=604800");

const options = {
  headers: reqHeaders,
};

// pass init as an "options" object with our headers
const req = new Request("flowers.jpg", options);

fetch(req).then((response) => {
  // ...
});

Note that you could also pass options into the fetch call to get the same effect, e.g.:

fetch(req, options).then((response) => {
  // ...
});

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

const options = {
  headers: {
    "Cache-Control": "max-age=60480",
  },
};

const req = new Request("flowers.jpg", options);

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.)

const copy = new Request(req);

• ServiceWorker API
• HTTP access control (CORS)
• HTTP