Philip Walton氏は、ブラウザがタブをアンロードしたときの対応方法をChrome開発者がコントロールするために、Chromeチームが取り組んでいる新しいAPIについて深く掘り下げています。

Application lifecycle is a key way that modern operating systems manage resources. On Android, iOS, and recent Windows versions, apps can be started and stopped at any time by the OS. This allows these platforms to streamline and reallocate resources where they best benefit the user.

On the web, there has historically been no such lifecycle, and apps can be kept alive indefinitely. With large numbers of web pages running, critical system resources such as memory, CPU, battery, and network can be oversubscribed, leading to a bad end-user experience.

While the web platform has long had events that related to lifecycle states — like load, unload, and visibilitychange — these events only allow developers to respond to user-initiated lifecycle state changes. For the web to work reliably on low-powered devices (and be more resource conscious in general on all platforms) browsers need a way to proactively reclaim and re-allocate system resources.

In fact, browsers today already do take active measures to conserve resources for pages in background tabs, and many browsers (especially Chrome) would like to do a lot more of this — to lessen their overall resource footprint.

The problem is developers currently have no way to prepare for these types of system-initiated interventions or even know that they’re happening. This means browsers need to be conservative or risk breaking web pages.

The Page Lifecycle API attempts to solve this problem by:

• Introducing and standardizing the concept of lifecycle states on the web.
• Defining new, system-initiated states that allow browsers to limit the resources that can be consumed by hidden or inactive tabs.
• Creating new APIs and events that allow web developers to respond to transitions to and from these new system-initiated states.
• This solution provides the predictability web developers need to build applications resilient to system interventions, and it allows browsers to more aggressively optimize system resources, ultimately benefiting all web users.

The rest of this post will introduce the new Page Lifecycle features shipping in Chrome 68 and explore how they relate to all the existing web platform states and events. It will also give recommendations and best-practices for the types of work developers should (and should not) be doing in each state.

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モバイルでは、ユーザーがブラウザを使用していないときにリソースを節約するために、ページをバックグラウンド（フリーズまたは破棄）するときにかなり攻撃的になる可能性があります（タブを入れ替えたり、AndroidのChromeアプリから移動するなど）あなたは伝統的にこれがいつ起こるのかを知らない開発者としてページを開いて、簡単に状態を保持したり、開いているリソースを閉じたりすることができず、アプリケーションが重要なときに状態をきれいに再水和します。開発者がコントロールできるようになると、情報に基づいた選択を行うことができ、ユーザーや開発者のエクスペリエンスに深刻な影響を与えることなく、ブラウザをより積極的に使用してリソースを節約できます。

最後に、下の図はそれをすべてうまく説明しています。