Textbox 自动调节高度

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();

        };

TextBox tbx_2 = new TextBox();

tbx_2.TextMode = TextBoxMode.MultiLine;

   tbx_2.ID = "tbx_2_" + tablerow_id;

        tbx_2.ClientIDMode = ClientIDMode.Static;        

 Page.ClientScript.RegisterStartupScript(this.GetType(), tbx_2.ID, "autoTextarea(document.getElementById('" + tbx_2.ID + "'));", true);