textarea自适应高度

gistfile1.js

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();
    };