textarea如何实现高度自适应？

今天需要些一个回复评论的页面，设计师给的初始界面就是一个只有一行的框。然后当时就想这个交互该怎么实现比较好，然后想起了新浪微博的做法：点击评论，默认显示一行，当输入的文字超过一行或者输入Enter时，输入框的高度会随着改变，直到输入完毕。顿时觉得这个细节做得挺不错的，可以效仿下。下面分享2种实现textarea高度自适应的做法，一种是用div来模拟textarea来实现的，用CSS控制样式，不用JS；另一种是利用JS控制的（因为存在浏览器兼容问题，所以写起来比较麻烦）；

方法0:textarea高度自适应，随着内容增加高度增加

$(function(){
        $.fn.autoHeight = function(){
        function autoHeight(elem){
            elem.style.height = 'auto';
            elem.scrollTop = 0; //防抖动
            elem.style.height = elem.scrollHeight + 'px';
        }
        this.each(function(){
            autoHeight(this);
            $(this).on('keyup', function(){
                autoHeight(this);
            });
        });
    }
    $('textarea[autoHeight]').autoHeight();
})

页面中的textarea直接加属性就行

<textarea  autoHeight="true" readonly="readonly" > </textarea>

pc   移动端都经过测试，没问题 放心用吧！出自：https://www.cnblogs.com/purple04551/p/8075366.html

方法一：div模拟textarea文本域轻松实现高度自适应

demo演示地址：http://www.xuanfengge.com/demo/201308/textarea/demo1.html

因为textarea不支持自适应高度，就是定好高度或者是行数之后，超出部分就会显示滚动条，看起来不美观。

而用DIV来模拟时，首先遇到的问题是：div怎么实现输入功能？

可能我们还是第一次见到这个属性contenteditable，如一个普通的block元素上加个contenteditable="true"就实现编辑，出现光标了。如

 

1	<div contenteditable="true"></div>

contenteditable属性虽是HTML5里面的内容，但是IE似乎老早就支持此标签属性了。所以，兼容性方面还是不用太担心的。

CSS代码

 

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.textarea{     width: 400px;     min-height: 20px;     max-height: 300px;     _height: 120px;     margin-left: auto;     margin-right: auto;     padding: 3px;     outline: 0;     border: 1px solid #a0b3d6;     font-size: 12px;     line-height: 24px;     padding: 2px;     word-wrap: break-word;     overflow-x: hidden;     overflow-y: auto;       border-color: rgba(82, 168, 236, 0.8);     box-shadow: inset 0 1px 3px rgba(0, 0, 0, 0.1), 0 0 8px rgba(82, 168, 236, 0.6); }

HTML代码

 

1	<div class="textarea" contenteditable="true"><br /></div>

CSS代码中，因为IE6不支持min/max，所以做了hack，其他的也好理解。

方法二：文本框textarea根据输入内容自适应高度

demo演示地址:http://www.xuanfengge.com/demo/201308/textarea/demo2.html

这个写法是用原生JS写的，考虑了很多兼容性问题，完全和新浪微博的回复效果一样的功能。有兴趣的童鞋可以仔细分析下代码。

CSS代码

 

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#textarea {     display: block;     margin:0 auto;     overflow: hidden;     width: 550px;     font-size: 14px;     height: 18px;     line-height: 24px;     padding:2px; } textarea {     outline: 0 none;     border-color: rgba(82, 168, 236, 0.8);     box-shadow: inset 0 1px 3px rgba(0, 0, 0, 0.1), 0 0 8px rgba(82, 168, 236, 0.6); }

JavaScript代码

 

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/** * 文本框根据输入内容自适应高度 * @param                {HTMLElement}        输入框元素 * @param                {Number}                设置光标与输入框保持的距离(默认0) * @param                {Number}                设置最大高度(可选) */ var autoTextarea = function (elem, extra, maxHeight) {         extra = extra || 0;         var isFirefox = !!document.getBoxObjectFor || 'mozInnerScreenX' in window,         isOpera = !!window.opera && !!window.opera.toString().indexOf('Opera'),                 addEvent = function (type, callback) {                         elem.addEventListener ?                                 elem.addEventListener(type, callback, false) :                                 elem.attachEvent('on' + type, callback);                 },                 getStyle = elem.currentStyle ? function (name) {                         var val = elem.currentStyle[name];                           if (name === 'height' && val.search(/px/i) !== 1) {                                 var rect = elem.getBoundingClientRect();                                 return rect.bottom - rect.top -                                         parseFloat(getStyle('paddingTop')) -                                         parseFloat(getStyle('paddingBottom')) + 'px';                                 };                           return val;                 } : function (name) {                                 return getComputedStyle(elem, null)[name];                 },                 minHeight = parseFloat(getStyle('height'));           elem.style.resize = 'none';           var change = function () {                 var scrollTop, height,                         padding = 0,                         style = elem.style;                   if (elem._length === elem.value.length) return;                 elem._length = elem.value.length;                   if (!isFirefox && !isOpera) {                         padding = parseInt(getStyle('paddingTop')) + parseInt(getStyle('paddingBottom'));                 };                 scrollTop = document.body.scrollTop || document.documentElement.scrollTop;                   elem.style.height = minHeight + 'px';                 if (elem.scrollHeight > minHeight) {                         if (maxHeight && elem.scrollHeight > maxHeight) {                                 height = maxHeight - padding;                                 style.overflowY = 'auto';                         } else {                                 height = elem.scrollHeight - padding;                                 style.overflowY = 'hidden';                         };                         style.height = height + extra + 'px';                         scrollTop += parseInt(style.height) - elem.currHeight;                         document.body.scrollTop = scrollTop;                         document.documentElement.scrollTop = scrollTop;                         elem.currHeight = parseInt(style.height);                 };         };           addEvent('propertychange', change);         addEvent('input', change);         addEvent('focus', change);         change(); };

HTML代码（写在body里面的）

 

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<textarea id="textarea" placeholder="回复内容"></textarea>     <script>         var text = document.getElementById("textarea");         autoTextarea(text);// 调用     </script>

文章来源：https://www.cnblogs.com/dffy/p/6386318.html

转自：http://www.xuanfengge.com/textarea-on-how-to-achieve-a-high-degree-of-adaptive.html

其他方法

• A different approach to elastic textareas
• Build an Elastic Textarea with Ext JS
• Smart TextArea: scrollHeight in IE, Firefox, Opera and Safari