A Cloudflare worker that allow cookie/path based caching.

worker.js

/**
 * Time-to-live in seconds for cached requests.
 */
const cacheTtl = 300;

/**
 * List of request paths to cache.
 */
const cachedPaths = [
    '/',
    '/about',
    '/contact',
];

addEventListener('fetch', event => {
    event.respondWith(fetchWithCacheTtl(event.request));
});

/**
 * Fetches the request after determining whether the request should
 * be cached and appends `X-Edge-Cache` to the response.
 *
 * @param {Request}
 * @return {Response}
 */
async function fetchWithCacheTtl(request) {
    const cacheRequest = requestShouldBeCached(request);

    const response = await fetch(request, {
        cf: { cacheTtl: cacheRequest ? cacheTtl : -1 }
    });

    let modifiedHeaders = new Headers(response.headers);

    modifiedHeaders.set('X-Edge-Cache', cacheRequest ? 'HIT' : 'BYPASS');

    return new Response(response.body, {
        status: response.status,
        statusText: response.statusText,
        headers: modifiedHeaders,
    });
}

/**
 * Determines whether the request should be cached.
 *
 * @param {Request}
 * @return {boolean}
 */
function requestShouldBeCached(request) {
    if (request.method !== 'GET') {
        return false;
    }

    const url = new URL(request.url);
    const path = url.pathname === '/' ? url.pathname : url.pathname.replace(/\/$/, '');

    if (! cachedPaths.includes(path)) {
        return false;
    }

    const cookies = request.headers.get('Cookie') || '';

    // The `batch` indicates whether a user is or was logged-in
    if (cookies.includes('batch')) {
        return false;
    }

    return true;
}