为什么代码不执行

来源：4-5 编程练习

六月青鸾

2019-09-08 00:09:54

<!DOCTYPE html>
<html>
<head lang="en">
        <meta charset="UTF-8">
        <title>输入文本</title>
    </head>
    <body>
        <p>字数限制在30字内，<span>您还可以输入<b>30</b> 字</span></p>
        <textarea cols="50"  rows="7"  id="text"></textarea>
        <script type="text/javascript">
            //补充代码
            var text=document.getElementById("text");
            var span=document.getElementsByTagName("span")[0];
            var total=30;
            var len=text.value.length;
            var allow=total-len;
            var beyond=len-total;
            text.onkeyup=function(){
                if(allow>=0){
                    span.innerHTML="您还可以输入"+allow+"字";
                }else{
                    span.innerHTML="您已超出"+beyond+"字";
                }
            }
        </script>
    </body>
</html>

写回答

1回答