浏览器会在以下情况时将请求加入队列，有优先级更高的请求；当请求协议是 HTTP/1.0 和 HTTP/1.1 时，同一域名下已经有 6 个 TCP 链接；浏览器在分配磁盘缓存
浏览器正在解析请求的 IP 地址
浏览器启动 service worker
Request to ServiceWorker
请求已经向 service worker 发出
浏览器等待第一个字节返回，此时间包括 1 次往返延迟和服务器准备响应所用的时间。
浏览器收到通过 HTTP/2 Server Push 的响应
Timing breakdown phases explained
Here’s more information about each of the phases you may see in the Timing tab:
The browser queues requests when:
- There are higher priority requests.
- There are already six TCP connections open for this origin, which is the limit. Applies to HTTP/1.0 and HTTP/1.1 only.
- The browser is briefly allocating space in the disk cache
The request could be stalled for any of the reasons described inQueueing.
The browser is resolving the request’s IP address.
The browser is negotiating the request with aproxy server.
The request is being sent.
The browser is starting up the service worker.
Request to ServiceWorker.
The request is being sent to the service worker.
The browser is waiting for the first byte of a response. TTFB stands for Time To First Byte. This timing includes 1 round trip of latency and the time the server took to prepare the response.
The browser is receiving the response.
The browser is receiving data for this response via HTTP/2 Server Push.
The browser is reading the local data previously received.