Element.scrollHeight

Element.scrollHeight 是计量元素内容高度的只读属性，包括overflow样式属性导致的视图中不可见内容。没有垂直滚动条的情况下，scrollHeight值与元素视图填充所有内容所需要的最小值clientHeight相同。包括元素的padding，但不包括元素的margin.

语法

var intElemScrollHeight = document.getElementById(id_attribute_value).scrollHeight;

intElemScrollHeight 存储着与元素scrollHeight像素值对应的一个整数。scrollHeight是一个只读属性。

用例

问题与解决方案

判定元素是否滚动到底

如果元素滚动到底，下面等式返回true，没有则返回false.

element.scrollHeight - element.scrollTop === element.clientHeight

scrollHeight 演示

监听onscroll事件，这个等式可以用来判定用户是否阅读过文本。（参考 element.scrollTop 和 element.clientHeight属性）。例如： 

HTML

<form name="registration">
  <p>
    <textarea id="rules">Lorem ipsum dolor sit amet, consectetur adipiscing elit. Vestibulum at laoreet magna. 
Aliquam erat volutpat. Praesent molestie, dolor ut eleifend aliquam, mi ligula ultrices sapien, quis cursus 
neque dui nec risus. Duis tincidunt lobortis purus eu aliquet. Quisque in dignissim magna. Aenean ac lorem at 
velit ultrices consequat. Nulla luctus nisi ut libero cursus ultrices. Pellentesque nec dignissim enim. Phasellus 
ut quam lacus, sed ultricies diam. Vestibulum convallis rutrum dolor, sit amet egestas velit scelerisque id. 
Proin non dignissim nisl. Sed mi odio, ullamcorper eget mattis id, malesuada vitae libero. Integer dolor lorem, 
mattis sed dapibus a, faucibus id metus. Duis iaculis dictum pulvinar. In nisi nibh, dapibus ac blandit at, porta 
at arcu. Pellentesque habitant morbi tristique senectus et netus et malesuada fames ac turpis egestas. Praesent 
dictum ipsum aliquet erat eleifend sit amet sollicitudin felis tempus. Aliquam congue cursus venenatis. Maecenas 
luctus pellentesque placerat. Mauris nisl odio, condimentum sed fringilla a, consectetur id ligula. Praesent sem 
sem, aliquet non faucibus vitae, iaculis nec elit. Nullam volutpat, lectus et blandit bibendum, nulla lorem congue 
turpis, ac pretium tortor sem ut nibh. Donec vel mi in ligula hendrerit sagittis. Donec faucibus viverra fermentum. 
Fusce in arcu arcu. Nullam at dignissim massa. Cras nibh est, pretium sit amet faucibus eget, sollicitudin in 
ligula. Vivamus vitae urna mauris, eget euismod nunc. Aenean semper gravida enim non feugiat. In hac habitasse 
platea dictumst. Cras eleifend nisl volutpat ante condimentum convallis. Donec varius dolor malesuada erat 
consequat congue. Donec eu lacus ut sapien venenatis tincidunt. Quisque sit amet tellus et enim bibendum varius et 
a orci. Donec aliquet volutpat scelerisque. Proin et tortor dolor. Ut aliquet, dolor a mattis sodales, odio diam 
pulvinar sem, egestas pretium magna eros vitae felis. Nam vitae magna lectus, et ornare elit. Morbi feugiat, ipsum 
ac mattis congue, quam neque mollis tortor, nec mollis nisl dolor a tortor. Maecenas varius est sit amet elit 
interdum quis placerat metus posuere. Duis malesuada justo a diam vestibulum vel aliquam nisi ornare. Integer 
laoreet nisi a odio ornare non congue turpis eleifend. Cum sociis natoque penatibus et magnis dis parturient montes, 
nascetur ridiculus mus. Cras vulputate libero sed arcu iaculis nec lobortis orci fermentum.
    </textarea>
  </p>
  <p>
    <input type="checkbox" name="accept" id="agree" />
    <label for="agree">I agree</label>
    <input type="submit" id="nextstep" value="Next" />
  </p>
</form>

CSS

#notice {
  display: inline-block;
  margin-bottom: 12px;
  border-radius: 5px;
  width: 600px;
  padding: 5px;
  border: 2px #7FDF55 solid;
}

#rules {
  width: 600px;
  height: 130px;
  padding: 5px;
  border: #2A9F00 solid 2px;
  border-radius: 5px;
}

JavaScript

function checkReading () {
  if (checkReading.read) {
    return; 
  }
  checkReading.read = this.scrollHeight - this.scrollTop === this.clientHeight;
  document.registration.accept.disabled = document.getElementById("nextstep").disabled = !checkReading.read;
  checkReading.noticeBox.innerHTML = checkReading.read ? "Thank you." : "Please, scroll and read the following text.";
}

onload = function () {
  var oToBeRead = document.getElementById("rules");
  checkReading.noticeBox = document.createElement("span");
  document.registration.accept.checked = false;
  checkReading.noticeBox.id = "notice";
  oToBeRead.parentNode.insertBefore(checkReading.noticeBox, oToBeRead);
  oToBeRead.parentNode.insertBefore(document.createElement("br"), oToBeRead);
  oToBeRead.onscroll = checkReading;
  checkReading.call(oToBeRead);
}

说明

scrollHeight MSIE's DHTML 对象模型的一部分. scrollHeight 是以下说明的一部分。: CSS Object Model (CSSOM) View Module.

浏览器兼容性

FIreFox < 21:  当元素内容并未产生垂直滚动条， scrollHeight 与 clientHeight 属性值相等。这可能表明，元素填充内容过少不需要垂直滚动条，或者CSS样式 overflow设置为visible。

参考资料

• MSDN: scrollHeight Property
• MSDN: Measuring Element Dimension and Location (Content moved.)
• MSDN: Measuring Element Dimension and Location with CSSOM in Windows Internet Explorer 9
• Element.clientHeight
• Element.offsetHeight
• Determining the dimensions of elements