在网络上发现一方法比较简单的实现文本框高度自适应，于是封装了这个函数，全兼容IE6+与现代浏览器！具体函数代码如下：
- /**
- * 文本框根据输入内容自适应高度
- **/
- var autoTextarea = function (elem, extra, maxHeight) {
- extra = extra || 20;
- 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.maxHeight = 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();
- };
调用方法如下（textarea_id为textarea的id值）：
- autoTextarea(document.getElementById('textarea_id'));
另外一种简易的实现方法：
- <html>
- <head>
- <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
- <title>TEXTAREA自适应文字行数的多少</title>
- </head>
- <body>
- <textarea rows="6" name="s1" cols="27" onpropertychange="this.style.posHeight=this.scrollHeight"></textarea>
- </body>
- </html>
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