---
title: A/B testing with same-URL direct access
description: Set up an A/B test by controlling what response is served based on cookies. This version supports passing the request through to test and control on the origin, bypassing random assignment.
image: https://developers.cloudflare.com/dev-products-preview.png
---

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# A/B testing with same-URL direct access

Set up an A/B test by controlling what response is served based on cookies. This version supports passing the request through to test and control on the origin, bypassing random assignment.

* [  JavaScript ](#tab-panel-11892)
* [  TypeScript ](#tab-panel-11893)
* [  Python ](#tab-panel-11894)
* [  Hono ](#tab-panel-11895)

JavaScript

```
const NAME = "myExampleWorkersABTest";
export default {  async fetch(req) {    const url = new URL(req.url);
    // Enable Passthrough to allow direct access to control and test routes.    if (url.pathname.startsWith("/control") || url.pathname.startsWith("/test"))      return fetch(req);
    // Determine which group this requester is in.    const cookie = req.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);  },};
```

TypeScript

```
const NAME = "myExampleWorkersABTest";
export default {  async fetch(req): Promise<Response> {    const url = new URL(req.url);    // Enable Passthrough to allow direct access to control and test routes.    if (url.pathname.startsWith("/control") || url.pathname.startsWith("/test"))      return fetch(req);    // Determine which group this requester is in.    const cookie = req.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);  },} satisfies ExportedHandler;
```

Python

```
import randomfrom urllib.parse import urlparse, urlunparsefrom workers import Response, fetch, WorkerEntrypoint
NAME = "myExampleWorkersABTest"
class Default(WorkerEntrypoint):  async def fetch(self, request):    url = urlparse(request.url)    # Uncomment below when testing locally    # url = url._replace(netloc="example.com") if "localhost" in url.netloc else url
    # Enable Passthrough to allow direct access to control and test routes.    if url.path.startswith("/control") or url.path.startswith("/test"):      return fetch(urlunparse(url))
    # Determine which group this requester is in.    cookie = request.headers.get("cookie")
    if cookie and f'{NAME}=control' in cookie:      url = url._replace(path="/control" + url.path)    elif cookie and f'{NAME}=test' in cookie:      url = url._replace(path="/test" + url.path)    else:      # If there is no cookie, this is a new client. Choose a group and set the cookie.      group = "test" if random.random() < 0.5 else "control"      if group == "control":        url = url._replace(path="/control" + url.path)      else:        url = url._replace(path="/test" + url.path)
      # Reconstruct response to avoid immutability      res = await fetch(urlunparse(url))      headers = dict(res.headers)      headers["Set-Cookie"] = f'{NAME}={group}; path=/'      return Response(res.body, headers=headers)
    return fetch(urlunparse(url))
```

TypeScript

```
import { Hono } from "hono";import { getCookie, setCookie } from "hono/cookie";
const app = new Hono();
const NAME = "myExampleWorkersABTest";
// Enable passthrough to allow direct access to control and test routesapp.all("/control/*", (c) => fetch(c.req.raw));app.all("/test/*", (c) => fetch(c.req.raw));
// Middleware to handle A/B testing logicapp.use("*", async (c) => {  const url = new URL(c.req.url);
  // Determine which group this requester is in  const abTestCookie = getCookie(c, NAME);
  if (abTestCookie === "control") {    // User is in control group    url.pathname = "/control" + c.req.path;  } else if (abTestCookie === "test") {    // User is in test group    url.pathname = "/test" + c.req.path;  } else {    // If there is no cookie, this is a new client    // Choose a group and set the cookie (50/50 split)    const group = Math.random() < 0.5 ? "test" : "control";
    // Update URL path based on assigned group    if (group === "control") {      url.pathname = "/control" + c.req.path;    } else {      url.pathname = "/test" + c.req.path;    }
    // Set cookie to enable persistent A/B sessions    setCookie(c, NAME, group, {      path: "/",    });  }
  const res = await fetch(url);
  return c.body(res.body, res);});
export default app;
```

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