javascript - 如何判断 XMLHTTPRequest 是否命中浏览器缓存

Question

是否可以判断(在 JavaScript 执行中)GET XMLHTTPRequest 是否命中浏览器缓存而不是从服务器获取响应？

Answer 1

来自XMLHttpRequest spec :

For 304 Not Modified responses that are a result of a user agent generated conditional request the user agent must act as if the server gave a 200 OK response with the appropriate content.

换句话说，浏览器将始终给出状态代码 200 OK，即使对于命中浏览器缓存的请求也是如此。

但是，规范还指出:

The user agent must allow author request headers to override automatic cache validation (e.g. If-None-Match or If-Modified-Since), in which case 304 Not Modified responses must be passed through.

因此，有一种解决方法可以使 304 Not Modified 响应对您的 JavaScript 代码可见。