如何检测元素是否具有“自动”高度

Question

window.getComputedStyle(element).height 和 element.clientHeight 都返回元素的当前高度（以像素为单位），无论 CSS 中设置的值如何。

有没有办法查出高度是设置为auto，还是像素以外的其他单位？

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@pvnarula 通过他链接的页面建议的一个解决方案是暂时change the contents of the element, then compare heights。 有点hacky...

Answer 1

请尝试：

document.getElementById("ele_id").style.height

同时检查以下插件：

http://gregpettit.ca/2012/jquery-check-if-element-has-auto-widthheight/

Answer 2

更新：

根据其他答案和大量在线研究，我想出了一个功能中的所有内容。在这里查看 jsfiddle： https://jsfiddle.net/oriadam/d01ap7r6/3/

// input a jQuery element
// return true for elements with auto height (90-100% is considered auto as well)
// return false for elements with fixed height
function is_height_auto($e) {
    var e = $e[0],
        // check fixed style:
        chk = function(value) {
            return /\d/.test(value) && !/^(100|9\d)\%/.test(value);
        };

    // start from the first, easiest, inline styles
    if (chk(e.style.height)) {
        // console.log('fixed for having style', e.style.height)
        return false;
    }

    // start from the first, easiest, inline styles
    var overflow = getComputedStyle(e)['overflow'];
    if (overflow == 'scroll' || overflow == 'auto' || (e.tagName == 'BODY' && overflow == 'visible')) {
        // console.log('auto for having overflow or is body', getComputedStyle(e)['overflow'], e.tagName);
        return true;
    }

    // deprecated chrome way - check each rule that applies to the element
    if (typeof getMatchedCSSRules == 'function') {
        var i, MatchedCSSRules = getMatchedCSSRules(e) || [];
        for (i = MatchedCSSRules.length; i; i--) {
            if (MatchedCSSRules[i - 1].style.height) {
                // console.log('found height at MatchedCSSRules[' + (i - 1) + ']: ', MatchedCSSRules[i - 1], ' All matches: ', MatchedCSSRules)
                return !chk(MatchedCSSRules[i - 1].style.height);
            }
        }
    }

    // append something, see if height was changed, remove the something
    var originalHeight = $e.height(),
        $ghost = jQuery('<b style="display:block;height:1px;width:1px;padding:0;margin:0;">').appendTo($e),
        newHeight = $e.height();
    $ghost.remove(); // cleanup
    // console.log('Using a ghost got ',newHeight > originalHeight,' originalHeight=' + originalHeight + ' newHeight=' + newHeight) 
    return newHeight > originalHeight;
} //is_height_auto()

** 鬼元素法解释（上一个答案）：**

Greg Pettit 有一个很好的答案in his blog，这里是主要思想：

自动高度有什么独特之处？好吧，它允许高度动态变化的事实，当然！

1. 克隆元素
2. 将其置于可见性：隐藏和位置：绝对
3. 删除它的内容
4. 查看高度是否改变（应该在 0 左右 现在）。

5. 清理

   var isAutoHeight = 函数（元素）{ // 为我们所有的工作创建一个暂存区。 $('body').append('');

   // assume false by default
   var autoHeight = false;
   
   // clone the div and move it; get its height
   var clone = element.clone();
   clone.appendTo('#stage');
   var initialHeight = clone.height();
   
   // destroy all the content and compare height
   clone.html('');
   var currentHeight = clone.height();
   if (currentHeight < initialHeight) {
       autoHeight = true;
   }
   
   // get that clone and its smelly duplicate ID out of the DOM!
   clone.remove();
   // do the same for the stage
   $('#stage').remove();
   
   return autoHeight;
   

   };

Answer 3

使用clone->heightCheck->remove innerHTML->heightCompare的方法遇到了一个bug。即使元素具有 100%/自动高度，它也不会记录高度变化。

相反，这种方法似乎有效：

let autoHeight = false;
// Set up stage area with 100% height/width
const stage = document.createElement('div');
      stage.setAttribute('style', "position: relative; height: 100%; width: 100%;");
// Add stage to body
document.body.appendChild(stage);
// Clone the element and append to stage
const clone = element.cloneNode(false);
stage.appendChild(clone);
// Get Initial Height
const initialHeight = clone.offsetHeight;
// Squish content
stage.setAttribute('style', "position: relative; height: 1px; width: 1px;");
// Get new height
const currentHeight = clone.offsetHeight;
// Get max height (if it exists)
const hasMaxHeight = getComputedStyle(clone)["maxHeight"];
// Compare
if (currentHeight < initialHeight && hasMaxHeight == 'none') {
  // Has 100% or auto height, and no maxHeight
} else if (hasMaxHeight !== 'none') {
  // Flexible, but has a maxHeight
} else {
  // Constrained by height size
}
// Remove elements
stage.remove();