文本框根据输入内容自适应高度的代码

/**
* 文本框根据输入内容自适应高度
* @author tang bin
* @version 0.3
* @see http://www.planeart.cn/?p=1489
* @param {HTMLElement} 输入框元素
* @param {Number} 设置光标与输入框保持的距离(默认20)
* @param {Number} 设置最大高度(可选)
*/
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();
};