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:

method

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

headers

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

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.

mode

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

credentials

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

cache

The cache mode you want to use for the request.

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).

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 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:

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():

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.:

fetch(myRequest, myOptions).then((response) => {
  // ...
});

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

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.)

const copy = new Request(myRequest);

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