A/B Testing

In this example of A/B Test, the response is sent to the same environment based on cookies. For example, if you are connected to the test environment from the test or control environment in the first request, you will be connected to the same test environment in subsequent requests.

const NAME = "myExampleWorkersABTest";

addEventListener("fetch", (event) => {
    event.respondWith(handleRequest(event.request));
});

async function handleRequest(request) {
  const url = new URL(request.url);

  // Enable Passthrough to allow direct access to control and test routes.
  if (url.pathname.startsWith("/control") || url.pathname.startsWith("/test"))
    return fetch(request);

  // Determine which group this requester is in.
  const cookie = request.headers.get("cookie");

  if (cookie && cookie.includes(`${NAME}=control`)) {
    url.pathname = "/control" + url.pathname;
  } else if (cookie && cookie.includes(`${NAME}=test`)) {
    url.pathname = "/test" + url.pathname;
  } else {
    // If there is no cookie, this is a new client. Choose a group and set the cookie.
    const group = Math.random() < 0.5 ? "test" : "control"; // 50/50 split
    if (group === "control") {
      url.pathname = "/control" + url.pathname;
    } else {
      url.pathname = "/test" + url.pathname;
    }
    // Reconstruct response to avoid immutability
    let res = await fetch(url);
    res = new Response(res.body, res);
    // Set cookie to enable persistent A/B sessions.
    res.headers.append("Set-Cookie", `${NAME}=${group}; path=/`);
    return res;
  }
  return fetch(url);
}