Experimental: This is an experimental technology
Check the Browser compatibility table carefully before using this in production.

Note: This feature is available in Web Workers.

The ContentIndex interface of the Content Index API allows developers to register their offline enabled content with the browser.

Instance properties

There are no properties of this interface.

Instance methods

ContentIndex.add() Experimental

Registers an item with the content index.

ContentIndex.delete() Experimental

Unregisters an item from the currently indexed content.

ContentIndex.getAll() Experimental

Returns a Promise that resolves with an iterable list of content index entries.


Feature detection and interface access

Here we get a reference to the ServiceWorkerRegistration, then check for the index property, which gives us access to the content index interface.

// reference registration
const registration = await navigator.serviceWorker.ready;

// feature detection
if ("index" in registration) {
  // Content Index API functionality
  const contentIndex = registration.index;

Adding to the content index

Here we're declaring an item in the correct format and creating an asynchronous function which uses the add() method to register it with the content index.

// our content
const item = {
  id: "post-1",
  url: "/posts/amet.html",
  title: "Amet consectetur adipisicing",
    "Repellat et quia iste possimus ducimus aliquid a aut eaque nostrum.",
  icons: [
      src: "/media/dark.png",
      sizes: "128x128",
      type: "image/png",
  category: "article",

// our asynchronous function to add indexed content
async function registerContent(data) {
  const registration = await navigator.serviceWorker.ready;

  // feature detect Content Index
  if (!registration.index) {

  // register content
  try {
    await registration.index.add(data);
  } catch (e) {
    console.log("Failed to register content: ", e.message);

Retrieving items within the current index

The below example shows an asynchronous function that retrieves items within the content index and iterates over each entry, building a list for the interface.

async function createReadingList() {
  // access our service worker registration
  const registration = await navigator.serviceWorker.ready;

  // get our index entries
  const entries = await registration.index.getAll();

  // create a containing element
  const readingListElem = document.createElement("div");

  // test for entries
  if (entries.length === 0) {
    // if there are no entries, display a message
    const message = document.createElement("p");
    message.innerText =
      "You currently have no articles saved for offline reading.";

  } else {
    // if entries are present, display in a list of links to the content
    const listElem = document.createElement("ul");

    for (const entry of entries) {
      const listItem = document.createElement("li");

      const anchorElem = document.createElement("a");
      anchorElem.innerText = entry.title;
      anchorElem.setAttribute("href", entry.url);



Unregistering indexed content

Below is an asynchronous function, that removes an item from the content index.

async function unregisterContent(article) {
  // reference registration
  const registration = await navigator.serviceWorker.ready;

  // feature detect Content Index
  if (!registration.index) return;

  // unregister content from index
  await registration.index.delete(;

All the above methods are available within the scope of the service worker. They are accessible from the WorkerGlobalScope.self property:

// service worker script



const contentIndexItems = self.registration.index.getAll();


Content Index
# content-index

Browser compatibility

BCD tables only load in the browser

See also