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

The SharedStorageOperation interface of the Shared Storage API represents the base class for all output gate operation types.

The output gate types are detailed below:

Name Description Defined by Invoked by
URL Selection Used to select a URL to display to the user based on shared storage data. SharedStorageSelectURLOperation selectURL()
Run A generic way to process some shared storage data. Used, for example, by the Private Aggregation API to process shared storage data and generate aggregated reports. SharedStorageRunOperation run()


Defining individual operations

Many shared storage worklet module scripts only define and register a single operation; you can see examples on the SharedStorageSelectURLOperation and SharedStorageRunOperation pages.

Defining multiple operations

In more advanced cases, it is possible to define and register multiple operations in the same shared storage worklet module script with different names. In the following worklet module script, we define a URL Selection operation called SelectURLOperation that selects a URL for A/B testing, and a Run operation called ExperimentGroupReportingOperation, which runs a histogram report based on the user's A/B testing group:

// ab-testing-worklet.js

class SelectURLOperation {
  async run(urls, data) {
    // Read the user's group from shared storage
    const experimentGroup = await sharedStorage.get("ab-testing-group");

    // Log to console for the demo
    console.log(`urls = ${JSON.stringify(urls)}`);
    console.log(`data = ${JSON.stringify(data)}`);
    console.log(`ab-testing-group in shared storage is ${experimentGroup}`);

    // Return the index of the group
    return data.indexOf(experimentGroup);

function getBucketForTestingGroup(testingGroup) {
  switch (testingGroup) {
    case "control":
      return 0;
    case "experiment-a":
      return 1;
    case "experiment-b":
      return 2;

class ExperimentGroupReportingOperation {
  async run() {
    const experimentGroup = await sharedStorage.get("ab-testing-group");

    const bucket = BigInt(getBucketForTestingGroup(experimentGroup));
    privateAggregation.contributeToHistogram({ bucket, value: 1 });

// Register the operations
register("ab-testing", SelectURLOperation);
register("experiment-group-reporting", ExperimentGroupReportingOperation);

In the main browsing context, these operations are invoked by selectURL() and run(), respectively. The operations to invoke via these methods are selected using the names they were registered with, and they are also required to conform to the structures defined by the SharedStorageSelectURLOperation and SharedStorageRunOperation classes and their run() methods.

// For demo purposes. The hostname is used to determine the usage of
// development localhost URL vs production URL
const contentProducerUrl =;

// Map the experiment groups to the URLs
    group: "control",
    url: `https://${contentProducerUrl}/ads/default-ad.html`,
    group: "experiment-a",
    url: `https://${contentProducerUrl}/ads/experiment-ad-a.html`,
    group: "experiment-b",
    url: `https://${contentProducerUrl}/ads/experiment-ad-b.html`,

// Choose a random group for the initial experiment
function getRandomExperiment() {
  const randomIndex = Math.floor(Math.random() * EXPERIMENT_MAP.length);
  return EXPERIMENT_MAP[randomIndex].group;

async function injectAd() {
  // Load the worklet module
  await window.sharedStorage.worklet.addModule("ab-testing-worklet.js");

  // Set the initial value in the storage to a random experiment group
  window.sharedStorage.set("ab-testing-group", getRandomExperiment(), {
    ignoreIfPresent: true,

  const urls ={ url }) => ({ url }));
  const groups ={ group }) => group);

  // Resolve the selectURL call to a fenced frame config only when it exists on the page
  const resolveToConfig = typeof window.FencedFrameConfig !== "undefined";

  // Run the URL selection operation to select an ad based on the experiment group in shared storage
  const selectedUrl = await window.sharedStorage.selectURL("ab-testing", urls, {
    data: groups,
    keepAlive: true,

  const adSlot = document.getElementById("ad-slot");

  if (resolveToConfig && selectedUrl instanceof FencedFrameConfig) {
    adSlot.config = selectedUrl;
  } else {
    adSlot.src = selectedUrl;

  // Run the reporting operation



Shared Storage API
# sharedstorageoperation

Browser compatibility

BCD tables only load in the browser

See also