---
title: A/B testing with middleware
description: Set up an A/B test by controlling what page is served based on cookies. This version supports passing the request through to test and control on the origin.
image: https://developers.cloudflare.com/dev-products-preview.png
---

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# A/B testing with middleware

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

JavaScript

```
const cookieName = "ab-test-cookie";const newHomepagePathName = "/test";
const abTest = async (context) => {  const url = new URL(context.request.url);  // if homepage  if (url.pathname === "/") {    // if cookie ab-test-cookie=new then change the request to go to /test    // if no cookie set, pass x% of traffic and set a cookie value to "current" or "new"
    let cookie = request.headers.get("cookie");    // is cookie set?    if (cookie && cookie.includes(`${cookieName}=new`)) {      // pass the request to /test      url.pathname = newHomepagePathName;      return context.env.ASSETS.fetch(url);    } else {      const percentage = Math.floor(Math.random() * 100);      let version = "current"; // default version      // change pathname and version name for 50% of traffic      if (percentage < 50) {        url.pathname = newHomepagePathName;        version = "new";      }      // get the static file from ASSETS, and attach a cookie      const asset = await context.env.ASSETS.fetch(url);      let response = new Response(asset.body, asset);      response.headers.append("Set-Cookie", `${cookieName}=${version}; path=/`);      return response;    }  }  return context.next();};
export const onRequest = [abTest];
```

```json
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```