节省流量

Network Information API：

https://wicg.github.io/netinfo/

https://github.com/mozilla/standards-positions/issues/117

Client Hints：

https://developers.google.com/web/updates/2015/09/automating-resource-selection-with-client-hints

// ua-clent-hint https://stackoverflow.com/questions/64413275/why-does-chrome-use-sec-ch-ua-not-abrandv-99

Save-Data 请求头以及 `navigator.connection.saveData`:https://developers.google.com/web/fundamentals/performance/optimizing-content-efficiency/save-data

// Vary 防止缓存