The fetch() method of the BackgroundFetchManager interface initiates a background fetch operation, given one or more URLs or Request objects.

Syntax

fetch(id, requests)
fetch(id, requests, options)

Parameters

id

A developer-defined identifier that can be passed to the other methods to retrieve the BackgroundFetchRegistration for this operation.

requests

A RequestInfo object or an array of RequestInfo objects.

Each RequestInfo object is a Request object or a string that will be given as the input argument to the Request() constructor.

options Optional

An object which will be used to customize the fetch progress dialog that the browser shows to the user. It has the following properties:

title Optional

A string that will be used as the title for the progress dialog.

icons Optional

An array of objects, each representing an icon that the browser may use for the progress dialog. Each object has the following properties:

src

A string representing a URL to the icon file.

sizes Optional

A string representing the sizes of the image, expressed using the same syntax as the sizes attribute of the <link> element.

type Optional

A string representing the MIME type of the icon.

label Optional

A string representing the accessible name of the icon.

downloadTotal Optional

A number representing the estimated total download size, in bytes, for the fetch operation. This is used to show the user how big the download is and to show the user download progress.

As soon as the total download size exceeds downloadTotal, then the fetch is aborted.

Return value

A Promise that resolves with a BackgroundFetchRegistration object.

Exceptions

TypeError

Raised if no request is provided, if the mode of a request is no-cors, if no service worker is present, a request already exists with the requested id, or the request fails.

AbortError DOMException

Indicates that the fetch was aborted.

NotAllowedError DOMException

Indicates that user permission has not been granted to make background fetches.

QuotaExceededError

Thrown if storing requests failed due to exceed the browser's storage quota.

Examples

The following example shows how to use fetch() to initiate a background fetch operation. With an active service worker, use the ServiceWorkerRegistration.backgroundFetch property to access the BackgroundFetchManager object and call its fetch() method.

navigator.serviceWorker.ready.then(async (swReg) => {
  const bgFetch = await swReg.backgroundFetch.fetch(
    "my-fetch",
    ["/ep-5.mp3", "ep-5-artwork.jpg"],
    {
      title: "Episode 5: Interesting things.",
      icons: [
        {
          sizes: "300x300",
          src: "/ep-5-icon.png",
          type: "image/png",
          label: "Downloading a show",
        },
      ],
      downloadTotal: 60 * 1024 * 1024,
    },
  );
});

Specifications

Browser compatibility