介绍
在理解DOM中的行数计数之前，让我们先了解一下DOM是什么？所以，DOM就像是HTML和XML文档的API。这个逻辑足以理解DOM对于Web开发人员来说是一个重要的概念。DOM为HTML和XML文档提供了编程接口，使程序员可以控制网页的结构、外观和内容。因此，在本文中，我们将看到如何在DOM元素中计算给定文本的行数。
Method 1: Using the scrollHeight Property
使用scrollHeight属性是一种确定DOM元素中包含多少文本行的技术。该属性返回元素作为整体的高度，包括任何被溢出隐藏的内容。我们可以通过将scrollHeight除以单行文本的高度来确定行数。
<!DOCTYPE html>
<html>
<body>
<div id="my-element">Lorem Ipsum is simply dummy text of the printing and typesetting industry.
Lorem Ipsum has been the industry's standard dummy text ever since the 1500s, when an unknown printer
took a galley of type and scrambled it to make a type specimen book. It has survived not only five
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popularised in the 1960s with the release of Letraset sheets containing Lorem Ipsum passages,
and more recently with desktop publishing software like Aldus PageMaker including
versions of Lorem Ipsum.
</div>
<div id="result"></div>
<script>
window.onload = function() {
let element = document.getElementById("my-element");
let fontSize = parseFloat(getComputedStyle(element).fontSize);
let numberOfLines = element.scrollHeight / fontSize;
document.getElementById("result").innerHTML = numberOfLines;
}
</script>
</body>
</html>
This code first selects the element with the id "my-element" and then uses getComputedStyle to obtain the font-size in pixels (element). You may determine how many lines of text are included in an element by taking its fontSize, parsing the value to float, and dividing the element's scrollHeight by fontSize.
需要注意的是，这种方法可能不完全准确，因为它依赖于字体大小在元素中保持恒定，并忽略了可能使用的任何额外间距或边距。此外，元素必须设置为overflow:visible，以使此技术正常工作。
方法2：使用clientHeight属性
使用clientHeight属性是另一种确定DOM元素中包含多少文本行的技术。该属性返回元素的高度，包括内容但不包括填充、边框和滚动条。我们可以通过将clientHeight除以单行文本的高度来获得行数。
<!DOCTYPE html>
<html>
<body>
<div id="my-element">
This code first select the element with id 'my-element' and gets the font-size in
pixels using getComputedStyle(element).fontSize and parse the value to float and divide
the scrollHeight of the element by fontSize which will give you the number of lines of
text inside the element. It's worth noting that this method may not be 100% accurate,
as it relies on the font size being consistent throughout the element and doesn't take
into account any additional spacing or margins that may be applied. Also, this method
only works if the element is set to have overflow:visible.
</div>
<div id="result"></div>
<script>
window.onload = function () {
let element = document.getElementById("my-element");
let fontSize = parseFloat(getComputedStyle(element).fontSize);
let numberOfLines = element.clientHeight / fontSize;
document.getElementById("result").innerHTML = numberOfLines;
};
</script>
</body>
</html>
We again select the element we want to count the lines of using document.getElementById("my-element"). We then use getComputedStyle(element).lineHeight to determine the height of a single line of text. Finally, we divide the element.clientHeight by the lineHeight to calculate the number of lines.
方法三：使用offsetHeight属性
通过使用offsetHeight属性，可以第三种方法来计算DOM元素内文本行的数量。该属性返回元素的高度，包括内容、填充和边框，但不包括滚动条。我们可以通过将offsetHeight除以单行文本的高度来确定行数。
<!DOCTYPE html>
<html>
<body>
<div id="my-element">There are many variations of passages of Lorem Ipsum available,
but the majority have suffered alteration in some form, by injected humour, or randomised words
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The generated Lorem Ipsum is therefore always free from repetition,
injected humour, or non-characteristic words etc.
</div>
<div id="result"></div>
<script>
window.onload = function() {
let element = document.getElementById("my-element");
let fontSize = parseFloat(getComputedStyle(element).fontSize);
let numberOfLines = Math.ceil(element.offsetHeight / fontSize);
document.getElementById("result").innerHTML = numberOfLines;
}
</script>
</body>
</html>
We again select the element we want to count the lines of using document.getElementById("my-element"). We then use getComputedStyle(element).lineHeight to determine the height of a single line of text. Finally, we divide the element.offsetHeight by the lineHeight to calculate the number of lines
请注意，这些方法仅计算元素内可见的文本行数，如果元素溢出并且具有滚动条，这些方法将无法计算不可见的文本行数。
如果我们想要计算包括不可见行在内的总行数，我们可以使用一个库，比如 text-line-count，它使用 range.getClientRects() 方法来确定总行数。
结论
本博客文章介绍了三种确定DOM元素中包含的文本行数的方法。每种方法通过将DOM元素的高度（由一个单独的属性确定）除以单行文本的高度来计算行数。您选择的方法将取决于项目的具体规格和主页的设计。无论选择哪种方法，都要记住这些估计可能不完全准确，因为它们基于单行文本的高度，而这可能会根据所选择的字体和大小而变化。
