Performing an A/B Test

In this example, cookies are used to store session information and perform A/B testing on requests. This example demonstrates how to use an edge function to perform A/B testing.

Sample Code

// cookie name
const COOKIE_NAME = 'ABTest';

// cookie value
const VALUE_A = 'index-a.html';
const VALUE_B = 'index-b.html';

// Root path, the origin must exist this path, and under this path, there are files index-a.html and index-b.html.
const BASE_PATH = '/abtest';

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

// Judge the URL path, if accessing non-abtest resources, directly responded.
if (!urlInfo.pathname.startsWith(BASE_PATH)) {
return fetch(request);

// Collected the current request's Cookie.
const cookies = new Cookies(request.headers.get('cookie'));
const abTestCookie = cookies.get(COOKIE_NAME);
const cookieValue = abTestCookie?.value;

// If the Cookie value is A test, Return index-a.html.
if (cookieValue === VALUE_A) {
urlInfo.pathname = `/${BASE_PATH}/${cookieValue}`;
return fetch(urlInfo.toString());

// If the Cookie value is B test, Return index-b.html.
if (cookieValue === VALUE_B) {
urlInfo.pathname = `/${BASE_PATH}/${cookieValue}`;
return fetch(urlInfo.toString());

// If the Cookie information does not exist, randomly grant the current request to A or B test.
const testValue = Math.random() < 0.5 ? VALUE_A : VALUE_B;
urlInfo.pathname = `/${BASE_PATH}/${testValue}`;

const response = await fetch(urlInfo.toString());

cookies.set(COOKIE_NAME, testValue, { path: '/', max_age: 60 });
response.headers.set('Set-Cookie', getSetCookie(cookies.get(COOKIE_NAME)));
return response;

// Concatenate Set-Cookie.
function getSetCookie(cookie) {
const cookieArr = [

const key2name = {
expires: 'Expires',
max_age: 'Max-Age',
domain: 'Domain',
path: 'Path',
secure: 'Secure',
httponly: 'HttpOnly',
samesite: 'SameSite',

Object.keys(key2name).forEach(key => {
if (cookie[key]) {

return cookieArr.join('; ');

addEventListener('fetch', event => {

Sample Preview

In the address bar of the browser, enter a URL that matches a trigger rule of the edge function to preview the effect of the sample code.