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

The SharedStorageSelectURLOperation interface of the Shared Storage API represents a URL Selection output gate operation.

Instance methods

run() Experimental

Defines the structure to which the run() method defined inside a URL Selection output gate operation should conform.


In this example, a class called SelectURLOperation is defined in a worklet and is registered using SharedStorageWorkletGlobalScope.register() with the name ab-testing. SharedStorageSelectURLOperation defines the structure to which this class needs to conform, essentially defining the parameters required for the run() method. Other than this requirement, the functionality of the class can be defined flexibly.

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

    // Return the group number
    return experimentGroup;

// Register the operation
register("ab-testing", SelectURLOperation);

Note: It is possible to define and register multiple operations in the same shared storage worklet module script with different names; see SharedStorageOperation for an example.

In the main browsing context, the ab-testing operation is invoked using the WindowSharedStorage.selectURL() method:

// 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(
      { 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;


For more details about this example and links to other examples, see the Shared Storage API landing page.


Shared Storage API
# sharedstorageselecturloperation

Browser compatibility

BCD tables only load in the browser

See also