The headers read-only property of the Request interface contains the Headers object associated with the request.

A Headers object.

In the following snippet, we create a new request using the Request() constructor (for an image file in the same directory as the script), then save the request headers in a variable:

const myRequest = new Request("flowers.jpg");
const myHeaders = myRequest.headers; // Headers {}

To add a header to the Headers object we use Headers.append; we then create a new Request along with a 2nd init parameter, passing headers in as an init option:

const myHeaders = new Headers();
myHeaders.append("Content-Type", "image/jpeg");

const myInit = {
  method: "GET",
  headers: myHeaders,
  mode: "cors",
  cache: "default",
};

const myRequest = new Request("flowers.jpg", myInit);

const myContentType = myRequest.headers.get("Content-Type"); // returns 'image/jpeg'

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