Facebook 與 Google Chrome 以及 Firefox 的人合作降低 Reload 使用的資源

Facebook 花了不少時間對付 reload 這件事情:「This browser tweak saved 60% of requests to Facebook」。

Facebook 的人發現有大量對靜態資源的 request 都是 304 (not modified) 回應:

In 2014 we found that 60% of requests for static resources resulted in a 304. Since content addressed URLs never change, this means there was an opportunity to optimize away 60% of static resource requests.

Google Chrome 很明顯偏高:

於是他們找出原因後,發現 Google Chrome 只要 POST 後的頁面都會 revalidate:

A piece of code in Chrome hinted at the answer to our question. This line of code listed a few reasons, including reload, for why Chrome might ask to revalidate resources on a page. For example, we found that Chrome would revalidate all resources on pages that were loaded from making a POST request.

然後在討論後認為這個行為不必要,就修掉了,可以看到降了非常多:

We worked with Chrome product managers and engineers and determined that this behavior was unique to Chrome and unnecessary. After fixing this, Chrome went from having 63% of its requests being conditional to 24% of them being conditional.

但還是很明顯比起其他瀏覽器偏高不少,在追問題後發現當輸入同樣的 url 時 (像是 Ctrl-L 或是 Cmd-L 然後直接按 enter),Google Chrome 會當作 reload:

The fact that the percentage of conditional requests from Chrome was still higher than other browsers seemed to indicate that we still had some opportunity here. We started looking into reloads and discovered that Chrome was treating same URL navigations as reloads while other browsers weren't.

不過這次推出修正後發現沒有大改變:(拿 production 測試 XDDD)

Chrome fixed the same URL behavior, but we didn't see a huge metric change. We began to discuss changing the behavior of the reload button with the Chrome team.

後來是針對 reload button 的行為修改,max-age 很長的就不 reload,比較短的就 reload。算是一種 workaround:

There was some debate about what to do, and we proposed a compromise where resources with a long max-age would never get revalidated, but that for resources with a shorter max-age the old behavior would apply. The Chrome team thought about this and decided to apply the change for all cached resources, not just the long-lived ones.

Google 也發了一篇說明這個新功能:「Reload, reloaded: faster and leaner page reloads」。

當 Facebook 的人找 Firefox 的人時,Firefox 決定另外定義哪些東西在 reload 時不需要 revalidate,而不像 Google Chrome 的 workaround:

Firefox chose to implement this directive in the form of a cache-control: immutable header.

Firefox 的人也寫了一篇「Using Immutable Caching To Speed Up The Web」解釋這個新功能。

所以之後規劃前後端的架構時又有東西要考慮進去...

用 BrowserSync 測試多個平台...

BrowserSync 是用 node.js 寫的工具,可以同時測試一堆 device,修改後不用按 reload,印象中已經有套件可以做類似的事情?

一般用 npm 裝就可以了:

npm install browser-sync

最簡單的方法是直接執行 browser-sync,執行後會出現像這樣的訊息:

<script src='//192.168.1.1:3000/socket.io/socket.io.js'></script>
<script>var ___socket___ = io.connect('http://192.168.1.1:3000');</script>
<script src='//192.168.1.1:3001/client/browser-sync-client.0.6.0.js'></script>

把這段程式碼貼到 body 的最後面就可以了,當 BrowerSync 偵測到檔案有更新時會透過 server push 機制重刷頁面。

另外,也可以產生 bs-config.js 修改設定:

browser-sync --init

更完整的說明可以從「Options」這頁找到。