textarea高度自動增高

隨着textarea 輸入內容 自動增長高度
<script type="text/javascript">

    $(".input_textarea").each(function(){
        this.style.height=this.scrollHeight+'px';
    });
    $(".input_textarea").bind({
        input:function(){
            this.style.height=this.scrollHeight + 'px';
        },
        propertychange:function(){
            this.style.height=this.scrollHeight + 'px';
        }
    });

</script>