textarea 高度根据内容自适应

1. <textarea style="width:420px;overflow-y:visible;"></textarea>
2. <textarea name="textarea" id="textarea" style='overflow-y: hidden;height:20px' onpropertychange="this.style.height = this.scrollHeight + 'px';" oninput="this.style.height = this.scrollHeight + 'px';"></textarea>