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---
title: 'Document: scroll事件'
slug: Web/API/Document/scroll_event
tags:
- API
- DOM
- Document
- Event
- 事件
- Reference
- 參考文件
- Scroll
- UIEvent
browser-compat: api.Document.scroll_event
---
{{APIRef}}
**`scroll`** 事件會在捲動文件的可視區域時觸發。元件（Element）捲動相關請參見{{domxref("Element/scroll_event", "Element: scroll事件")}}。
<table class="properties">
<tbody>
<tr>
<th>Bubbles</th>
<td>是</td>
</tr>
<tr>
<th>Cancelable</th>
<td>否</td>
</tr>
<tr>
<th>介面</th>
<td>{{DOMxRef("Event")}}</td>
</tr>
<tr>
<th>事件處理常式的屬性</th>
<td>
{{DOMxRef("GlobalEventHandlers.onscroll", "onscroll")}}
</td>
</tr>
</tbody>
</table>
> **註：**iOS的UIWebViews中，`scroll`事件不會在捲動時觸發，而只在捲動結束後觸發。請參見[Bootstrap issue #16202](https://github.com/twbs/bootstrap/issues/16202)。Safari和WKWebViews不受本bug影響。
## 範例
### 限制捲動事件的觸發次數
Since scroll events can fire at a high rate, the event handler shouldn't execute computationally expensive operations such as DOM modifications. Instead, it is recommended to throttle the event using requestAnimationFrame(), setTimeout(), or a CustomEvent, as follows.
Note, however, that input events and animation frames are fired at about the same rate, and therefore the optimization below is often unnecessary. This example optimizes thescroll event for requestAnimationFrame.
有鑒於`scroll`事件可能會以很高的速率觸發，事件處理常式不應執行計算密集的操作（如DOM修改）。所以，建議改用{{DOMxRef("Window.requestAnimationFrame()", "requestAnimationFrame()")}}、{{DOMxRef("setTimeout()")}}或{{DOMxRef("CustomEvent")}}以調控事件的觸發次數，如下。
不過需要注意，輸入事件和動畫影格的觸發速率大致相同，因此通常沒有必要進行下述的最佳化。本範例最佳化`requestAnimationFrame`的`scroll`事件。
```js
// 參考來源：http://www.html5rocks.com/en/tutorials/speed/animations/
let lastKnownScrollPosition = 0;
let ticking = false;
function doSomething(scrollPos) {
// 依據捲動位置進行某些操作
}
document.addEventListener('scroll', function(e) {
lastKnownScrollPosition = window.scrollY;
if (!ticking) {
window.requestAnimationFrame(function() {
doSomething(lastKnownScrollPosition);
ticking = false;
});
ticking = true;
}
});
```
更多類似範例可見[`resize`](/zh-TW/docs/Web/API/Window/resize_event)事件頁面。
## 規格
{{Specifications}}
## 瀏覽器相容性
{{Compat}}
## 延伸閱讀
- [Element: `scroll`事件](/zh-TW/docs/Web/API/Element/scroll_event)
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