ETag 与 Last-Modified 条件请求与一致性实践

概述条件请求在资源未变更时返回 304，保持缓存与服务器一致。本文示例前端如何协作。条件请求async function revalidate(url, cached) {

const etag = cached.headers.get('ETag') || '';

const lm = cached.headers.get('Last-Modified') || '';

const headers = {};

if (etag) headers['If-None-Match'] = etag;

if (lm) headers['If-Modified-Since'] = lm;

const res = await fetch(url, { headers });

return res;

}