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

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

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

icons

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

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

type

A string representing the MIME type of the icon. Optional

label

A string representing the accessible name of the icon. Optional

downloadTotal

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.

A Promise that resolves with a BackgroundFetchRegistration object.

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.

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,
    },
  );
});