Response

The Response interface of the Fetch API represents the response to a request.

You can create a new Response object using the Response.Response() constructor, but you are more likely to encounter a Response object being returned as the result of another API operation—for example, a service worker Fetchevent.respondWith, or a simple WindowOrWorkerGlobalScope.fetch().

Response()

Creates a new Response object.

Response.headers Read only

The Headers object associated with the response.

Response.ok Read only

A boolean indicating whether the response was successful (status in the range 200–299) or not.

Response.redirected Read only

Indicates whether or not the response is the result of a redirect (that is, its URL list has more than one entry).

Response.status Read only

The status code of the response. (This will be 200 for a success).

Response.statusText Read only

The status message corresponding to the status code. (e.g., OK for 200).

Response.trailers

A Promise resolving to a Headers object, associated with the response with Response.headers for values of the HTTP Trailer header.

Response.type Read only

The type of the response (e.g., basic, cors).

Response.url Read only

The URL of the response.

Response.useFinalURL

A boolean indicating whether this is the final URL of the response.

Response implements Body, so it also has the following properties available to it:

Body.body Read only

A simple getter exposing a ReadableStream of the body contents.

Body.bodyUsed Read only

Stores a Boolean that declares whether the body has been used in a response yet.

Response.clone()

Creates a clone of a Response object.

Response.error()

Returns a new Response object associated with a network error.

Response.redirect()

Creates a new response with a different URL.

Response implements Body, so it also has the following methods available to it:

Body.arrayBuffer()

Takes a Response stream and reads it to completion. It returns a promise that resolves with an ArrayBuffer.

Body.blob()

Takes a Response stream and reads it to completion. It returns a promise that resolves with a Blob.

Body.formData()

Takes a Response stream and reads it to completion. It returns a promise that resolves with a FormData object.

Body.json()

Takes a Response stream and reads it to completion. It returns a promise that resolves with the result of parsing the body text as JSON, which is a JavaScript value of datatype object, string, etc.

Body.text()

Takes a Response stream and reads it to completion. It returns a promise that resolves with a USVString (text).

In our basic fetch example (run example live) we use a simple fetch() call to grab an image and display it in an <img> element. The fetch() call returns a promise, which resolves to the Response object associated with the resource fetch operation.

You'll notice that since we are requesting an image, we need to run Body.blob (Response implements Body) to give the response its correct MIME type.

const image = document.querySelector('.my-image');
fetch('flowers.jpg').then(function(response) {
  return response.blob();
}).then(function(blob) {
  const objectURL = URL.createObjectURL(blob);
  image.src = objectURL;
});

You can also use the Response.Response() constructor to create your own custom Response object:

const response = new Response();

Here we call a PHP program file that generates a JSON string, displaying the result as a JSON value, including simple error handling.

// Function to do an Ajax call
const doAjax = async () => {
    const response = await fetch('Ajax.php'); // Generate the Response object
    if (response.ok) {
        const jVal = await response.json(); // Get JSON value from the response body
        return Promise.resolve(jVal);
        }
    else {
        return Promise.reject('*** PHP file not found');
    }
}

// Call the function and output value or error message to console
doAjax().then(console.log).catch(console.log);

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