js实现textarea根据内容大小自适应高度

首先，我们来看看源代码：

/*** 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) {//判断elem是否为数组if(elem.length > 0){for(var i = 0; i < elem.length; i++ ){e(elem[i]);}}else{e(elem);}function e(elem){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();}};

把上面的代码复制之后引入到你的网页里面，然后就可以用了。

假设你有一个id为T 的textarea文本域，那么就可以进行以下绑定：

var T = document.getElementById("T");

autoTextarea(T);

或者直接这样：

autoTextarea(document.getElementById("T"));

如果是数组的话，就是这样：

autoTextarea(document.getElementsByClassName("T"));

如果是用Jquery的话，由于Jquery获取的Id对象本身会变成一个数组，所以想要取得和js一样的对象，必须加[0]，示例如下：

var T = $("#T");

autoTextarea(T[0]);

如果是class的时候则不需要进行修改，和直接用document.getElementsByClassName()的情况是一样的。

如：autoTextarea($(".T"));