如何使用 JavaScript 获取 <textarea > 中的行数？

Question

我有一个<textarea> 元素。我可以使用 JavaScript 来检测其中有（例如）10 行文本吗？

Answer 1

我找到了一种更简单的方法来做到这一点，但是您需要在 CSS 中设置 textarea 的 line-height。我试图读取脚本ta.style.lineHeight 中的行高，但它似乎没有返回值。

CSS

#ta { width: 300px; line-height: 20px; }

HTML

<textarea id="ta">Lorem ipsum dolor sit amet, consectetur adipiscing elit. Quisque suscipit, nisl eget dapibus condimentum, ipsum felis condimentum nisi, eget luctus est tortor vitae nunc. Nam ornare dictum augue, non bibendum sapien pulvinar ut. Vestibulum ante ipsum primis in faucibus orci luctus et ultrices posuere cubilia Curae; Cras congue congue purus, quis imperdiet tellus ornare in. Nulla facilisi. Nulla elementum posuere odio ut ultricies. Nullam tempus tincidunt elit eget posuere. Pellentesque sit amet tellus sapien. Praesent sed iaculis turpis. Nam quis nibh diam, sed mattis orci. Nullam ornare adipiscing congue. In est orci, consectetur in feugiat non, consequat vitae dui. Mauris varius dui a dolor convallis iaculis.</textarea>

脚本

 var taLineHeight = 20; // This should match the line-height in the CSS
 var taHeight = ta.scrollHeight; // Get the scroll height of the textarea
 ta.style.height = taHeight; // This line is optional, I included it so you can more easily count the lines in an expanded textarea
 var numberOfLines = Math.floor(taHeight/taLineHeight);
 alert( "there are " + numberOfLines + " lines in the text area");

---

更新：感谢@Pebbl 解决错误，这是获取文本内容高度所需的代码 (demo)

var calculateContentHeight = function( ta, scanAmount ) {
    var origHeight = ta.style.height,
        height = ta.offsetHeight,
        scrollHeight = ta.scrollHeight,
        overflow = ta.style.overflow;
    /// only bother if the ta is bigger than content
    if ( height >= scrollHeight ) {
        /// check that our browser supports changing dimension
        /// calculations mid-way through a function call...
        ta.style.height = (height + scanAmount) + 'px';
        /// because the scrollbar can cause calculation problems
        ta.style.overflow = 'hidden';
        /// by checking that scrollHeight has updated
        if ( scrollHeight < ta.scrollHeight ) {
            /// now try and scan the ta's height downwards
            /// until scrollHeight becomes larger than height
            while (ta.offsetHeight >= ta.scrollHeight) {
                ta.style.height = (height -= scanAmount)+'px';
            }
            /// be more specific to get the exact height
            while (ta.offsetHeight < ta.scrollHeight) {
                ta.style.height = (height++)+'px';
            }
            /// reset the ta back to it's original height
            ta.style.height = origHeight;
            /// put the overflow back
            ta.style.overflow = overflow;
            return height;
        }
    } else {
        return scrollHeight;
    }
}

var calculateHeight = function() {
    var ta = document.getElementById("ta"),
        style = (window.getComputedStyle) ?
            window.getComputedStyle(ta) : ta.currentStyle,

        // This will get the line-height only if it is set in the css,
        // otherwise it's "normal"
        taLineHeight = parseInt(style.lineHeight, 10),
        // Get the scroll height of the textarea
        taHeight = calculateContentHeight(ta, taLineHeight),
        // calculate the number of lines
        numberOfLines = Math.ceil(taHeight / taLineHeight);

    document.getElementById("lines").innerHTML = "there are " +
        numberOfLines + " lines in the text area";
};

calculateHeight();
if (ta.addEventListener) {
    ta.addEventListener("mouseup", calculateHeight, false);
    ta.addEventListener("keyup", calculateHeight, false);
} else if (ta.attachEvent) { // IE
    ta.attachEvent("onmouseup", calculateHeight);
    ta.attachEvent("onkeyup", calculateHeight);
}

Answer 2

只有一行js：

var rows = document.querySelector('textarea').value.split("\n").length;

Answer 3

假设您知道行高，最简单的方法是：

function numOfLines(textArea, lineHeight) {
    var h0 = textArea.style.height;
    ta.style.height = 'auto';
    var h1 = textArea.scrollHeight;
    textArea.style.height = h0;
    return Math.ceil(h1 / lineHeight);
}

这里的技巧是首先将高度设置为auto。然后，当您访问 scrollHeight 时，浏览器将进行布局并返回正确的高度，包括任何换行。然后将textarea高度恢复到原来的值并返回结果。

Answer 4

你可以从Element.scrollHeight得到实际的文字高度，但是要得到正确的高度，必须要有一个滚动条，也就是说你可以暂时将文本框高度设置为0，直到得到滚动条高度值，然后恢复 CSS 高度。

你有一个，你根据 CSS line-height 属性值计算行数（1 行文本贡献getComputedStyle(ref).lineHeight 像素），类似于...

function getTextareaNumberOfLines(textarea) {
    var previous_height = textarea.style.height, lines
    textarea.style.height = 0
    lines = parseInt( textarea.scrollHeight/parseInt(getComputedStyle(textarea).lineHeight) )
    textarea.style.height = previous_height
    return lines
}

注意：您的元素必须存在于 DOM 中才能获取 scrollHeight、lineHeight 高度等。如果尚未存在，请添加它们，计算值，然后从 DOM 中删除它们。

Answer 5

    function countLines(area,maxlength) {
       // var area = document.getElementById("texta")
        // trim trailing return char if exists
        var text = area.value.replace(/\s+$/g, "")
        var split = text.split("\n")
        if (split.length > maxlength) {
            split = split.slice(0, maxlength);
            area.value = split.join('\n');
            alert("You can not enter more than "+maxlength.toString()+" lines");
        }
        return false;
    }

这是一个简单且经过测试的

Answer 6

您可以通过 Javascript DOM 访问该字段并简单地计算换行符的数量。

oArea = document.getElementById('myTextField');
var aNewlines = oArea.value.split("\n");
var iNewlineCount = aNewlines.length();

Answer 7

简单的方法：

var lines = document.querySelector("textarea").value.split(/\r\n|\r|\n/).length;