<textarea rows="5" maxlength="200" onchange="this.value=this.value.substring(0, 200)" onkeydown="this.value=this.value.substring(0, 200)" onkeyup="this.value=this.value.substring(0, 200)" ></textarea>
来源：https://www.cnblogs.com/duzjextjs/p/5915405.html