在理解DOM中的行數計數之前，讓我們先了解一下DOM是什麼？所以，DOM就像是HTML和XML文件的API。這個邏輯足以理解DOM對Web開發人員來說是一個重要的概念。 DOM為HTML和XML文件提供了程式設計接口，使程式設計師可以控制網頁的結構、外觀和內容。因此，在本文中，我們將看到如何在DOM元素中計算給定文字的行數。
使用scrollHeight屬性是一種決定DOM元素中包含多少文字行的技術。此屬性傳回元素作為整體的高度，包括任何被溢出隱藏的內容。我們可以將scrollHeight除以單行文字的高度來確定行數。
<!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
centuries, but also the leap into electronic typesetting, remaining essentially unchanged. It was
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 elits by , parsing the value to float, and dividing the element's scrollHeight by fontSize.
需要注意的是，這種方法可能不完全準確，因為它依賴於字體大小在元素中保持恆定，並忽略了可能使用的任何額外間距或邊距。此外，元素必須設定為overflow:visible，以使此技術正常運作。
使用clientHeight屬性是另一個決定DOM元素中包含多少文字行的技術。此屬性傳回元素的高度，包括內容但不包括填滿、邊框和捲軸。我們可以將clientHeight除以單行文字的高度來獲得行數。
<!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. divide the element.clientHeight by the lineHeight to calculate the number of lines.
透過使用offsetHeight屬性，可以第三種方法來計算DOM元素內文字行的數量。此屬性傳回元素的高度，包括內容、填滿和邊框，但不包括捲軸。我們可以將offsetHeight除以單行文字的高度來確定行數。
<!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
which don't look even slightly believable. If you are going to use a passage of Lorem Ipsum, you
need to be sure there isn't anything embarrassing hidden in the middle of text. All the Lorem
Ipsum generators on the Internet tend to repeat predefined chunks as necessary, making this the
first true generator on the Internet. It uses a dictionary of over 200 Latin words, combined
with a handful of model sentence structures, to generate Lorem Ipsum which looks reasonable.
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. divide the element.offsetHeight by the lineHeight to calculate the number of lines
請注意，這些方法僅計算元素內可見的文字行數，如果元素溢出並且具有捲軸，這些方法將無法計算不可見的文字行數。
如果我們想要計算包含不可見行在內的總行數，我們可以使用一個函式庫，例如 text-line-count，它使用 range.getClientRects() 方法來決定總行數。
本部落格文章介紹了三種確定DOM元素中包含的文字行數的方法。每種方法透過將DOM元素的高度（由一個單獨的屬性決定）除以單行文字的高度來計算行數。您選擇的方法將取決於項目的特定規格和主頁的設計。無論選擇哪種方法，都要記住這些估計可能不完全準確，因為它們基於單行文字的高度，而這可能會根據所選的字體和大小而變化。
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