The Page Visibility API用於檢測(cè)網(wǎng)頁是否對(duì)用戶可見。它通過document.visibilityState屬性返回頁面的可見狀態(tài)，包括visible、hidden和prerender三種值，並支持通過visibilitychange事件監(jiān)聽狀態(tài)變化。 1.可用於暫停媒體播放、停止後臺(tái)任務(wù)以節(jié)省資源；2.提高用戶參與度跟蹤準(zhǔn)確性；3.智能更新內(nèi)容如刷新新聞feed。實(shí)現(xiàn)方式是添加visibilitychange事件監(jiān)聽器並根據(jù)visibilityState值執(zhí)行相應(yīng)操作。使用時(shí)應(yīng)注意兼容性問題及不同瀏覽器的行為差異，建議結(jié)合其他API進(jìn)行性能優(yōu)化。

When you're building a website or web app, knowing whether a page is visible to the user can be super useful. That's where the Page Visibility API comes in — it lets you check if a page is currently visible and react accordingly.

What does the Page Visibility API do?

At its core, this API helps you determine the visibility state of a webpage. The main property you'll work with is document.visibilityState , which can return one of three values:

• visible – the page is at least partially visible
• hidden – the page isn't visible (user switched tabs, minimized browser, etc.)
• prerender – the page is being preloaded but not fully visible yet (not always used)

You don't need any special setup to use it — just check the value or listen for changes using the visibilitychange event.

Why would you use it?

There are several real-world cases where knowing visibility status makes a difference:

• Pause videos/audio when the user isn't looking, then resume when they come back
• Stop animations or background tasks to save CPU/GPU resources
• Track user engagement more accurately by measuring actual viewing time
• Update content smartly , like refreshing news feeds only when the tab becomes active again

It's especially handy for apps that run in the background but should only do heavy lifting when needed.

How to implement it

Using the API is pretty straightforward. Here's how you'd typically set it up:

 document.addEventListener('visibilitychange', function () {
  if (document.visibilityState === 'hidden') {
    // Do something when page is not visible
  } else if (document.visibilityState === 'visible') {
    // Do something when page becomes visible
  }
});

A few tips:

• You might want to debounce or throttle updates if visibility changes often (like switching tabs quickly)
• Combine it with other APIs like requestIdleCallback or IntersectionObserver for smarter performance tuning
• Don't rely on it for critical functionality — some older browsers may not support it fully

One thing to watch out for

While the API works well in most modern browsers, keep in mind how different environments handle visibility. For example, iOS Safari has had some quirks in the past where background tabs still report as "visible". Testing across devices is always a good idea, especially if your app relies heavily on accurate visibility tracking.

基本上就這些. It's not complicated, but knowing when users are actually looking at your page opens up a lot of optimization and UX possibilities.

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