Element.scrollTop

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Element.scrollTop 屬性可以設置和獲取元素被向上捲動的高度(pixels). 元素的 scrollTop 是元素頂端和能被看見的最頂端之間的距離. 當元素並未產生滾動條, 那麼 scrollTop 的值預設為 0.

表達式

js
// 獲得已經被滾動的距離(pixels)
var intElemScrollTop = someElement.scrollTop;

intElemScrollTop 為 element已經被滾動的距離(pixels ).

js
// 設置已經被滾動的距離(pixels)
element.scrollTop = intValue;

scrollTop 可以被設置為任何和正整數, 注意事項:

  • 如果元素不能滾動, scrollTop 被設置為 0.
  • 如果設置的值小於 0, scrollTop 被設置為 0.
  • 如果設置的值大於內容可以被滾動的距離, scrollTop 被設置為最大值.

範例

Scrolling an element

In this example, try scrolling the inner container with the dashed border, and see how the value of scrollTop changes.

HTML

html
<div id="container">
  <div id="scroller">
    <p>
      Far out in the uncharted backwaters of the unfashionable end of the
      western spiral arm of the Galaxy lies a small unregarded yellow sun.
      Orbiting this at a distance of roughly ninety-two million miles is an
      utterly insignificant little blue green planet whose ape-descended life
      forms are so amazingly primitive that they still think digital watches are
      a pretty neat idea.
    </p>
  </div>
</div>

<div id="output">scrollTop: 0</div>

CSS

css
#scroller {
  overflow: scroll;
  height: 150px;
  width: 150px;
  border: 5px dashed orange;
}

#output {
  padding: 1rem 0;
}

JavaScript

js
const scroller = document.querySelector("#scroller");
const output = document.querySelector("#output");

scroller.addEventListener("scroll", (event) => {
  output.textContent = `scrollTop: ${scroller.scrollTop}`;
});

結果

規範

Specification
CSSOM View Module
# dom-element-scrolltop

參閱