Run A/B Testing

Use a Shared Storage worklet to run A/B testing.

The Shared Storage API is a Privacy Sandbox proposal for general purpose, cross-site storage, which supports many possible use cases. One such example is A/B testing, which is available to test in Chrome 104.0.5086.0 and later.

You can assign a user to an experiment group, then store that group in Shared Storage to be accessed in a cross-site environment.

Try A/B testing

To experiment with A/B testing with Shared Storage, confirm you're using Chrome 104.0.5086.0 or later. Enable all the Ad privacy APIs under chrome://settings/adPrivacy.

You can also enable Shared Storage with the --enable-features=PrivacySandboxAdsAPIsOverride,OverridePrivacySandboxSettingsLocalTesting,SharedStorageAPI,FencedFrames flag in the command line.

Experiment with code samples

To see if an experiment has the desired effect, you can run A/B testing across multiple sites. As an advertiser or a content producer, you can choose to render different content or ads based on what group the user is assigned to. The group assignment is saved in shared storage, but cannot be exfiltrated.

In this example:

  • ab-testing.js should be embedded in a frame, which maps a control and two experiment contents. The script calls the shared storage worklet for the experiment.
  • ab-testing-worklet.js is the shared storage worklet that returns which group the user is assigned to, determining which ad is shown.

ab-testing.js

// Randomly assigns a user to a group 0 or 1
function getExperimentGroup() {
  return Math.round(Math.random());
}

async function injectContent() {
  // Register the Shared Storage worklet
  await window.sharedStorage.worklet.addModule('ab-testing-worklet.js');

  // Assign user to a random group (0 or 1) and store it in Shared Storage
  window.sharedStorage.set('ab-testing-group', getExperimentGroup(), {
    ignoreIfPresent: true,
  });

  // Run the URL selection operation
  const fencedFrameConfig = await window.sharedStorage.selectURL(
    'ab-testing',
    [
      { url: `https://your-server.example/content/default-content.html` },
      { url: `https://your-server.example/content/experiment-content-a.html` }
    ],
    {
      resolveToConfig: true
    }
  );

  // Render the chosen URL into a fenced frame
  document.getElementById('content-slot').config = fencedFrameConfig;
}

injectContent();

ab-testing-worklet.js

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

    // Return the corresponding URL (first or second item in the array)
    return urls.indexOf(experimentGroup);
  }
}

register('ab-testing', SelectURLOperation);

Engage and share feedback

Note that the Shared Storage API proposal is under active discussion and development and therefore subject to change.

We're eager to hear your thoughts on the Shared Storage API.

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