onKeyUp 事件 在键盘按键被松开时触发

<textarea id="mytext1" name="deal_descript" onkeyup="textLen()"></textarea>
<p class="pos2"><span>0</span>/50</p>

function textLen(){
var inputText = document.getElementById('mytext1').value;
if(inputText.length > 50){
var text = inputText.substring(0,50);
alertStr("最多输入50个字");
document.getElementById('mytext1').value = text;
$(".pos2 span").html(inputText.length);
die();
}
$(".pos2 span").html(inputText.length);
}