HTTP 304 未改变说明无需再次传输请求的内容，也就是说可以使用缓存的内容。这通常是在一些安全的方法（safe），例如GET 或HEAD 或在请求中附带了头部信息： If-None-Match 或If-Modified-Since。
If the equivalent 200 OK response would have included the headers Cache-Control, Content-Location, Date, ETag, Expires, and Vary.
Many developer tools' network panels of browsers create extraneous requests leading to 304 responses, so that access to the local cache is visible to developers.
状态
304 Not Modified
标准
| 标准 | 标题 |
|---|---|
| RFC 7232, section 4.1: 304 Not Modified | Hypertext Transfer Protocol (HTTP/1.1): Conditional Requests |
浏览器兼容
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