The code is as follows
<script language="JavaScript">
function check(){
var tx=document.form1.username.value;
var d=document.getElementById("p1");
if (!tx.match("^[a-zA-Z0-9_]{10,13}$")) {
d.outerText="你输入的用户名非法!";
}
else{
d.style.visibility ="hidden";
}
}
</script>
</head>
<body>
<form name="form1">
用户名：<input type="text" name="username" onmouseleave="return check()"/>
<p id="p1">请输入5到10为用户名！</p>
</form>
</body>Prompt: Line: 13 Error: 'null' is empty or not an object, how to solve it?
Solution:
Change d.outerText="you enter The username you entered is illegal!";
Changed to
d.innerHTML="The username you entered is illegal!";
Because after your outerText, p no longer exists.
innerText
innerHTML changes the content inside
outer changes the outside. Even the label has been replaced and it won’t work next time. So it is null
![[Web front-end] Node.js quick start](https://img.php.cn/upload/course/000/000/067/662b5d34ba7c0227.png)
