在线运行代码 - 菜鸟教程

<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>菜鸟教程(cainiaoplay.com)</title>
</head>
<body>

<form action="tryjs_submitpage.htm" onsubmit="return myFunction()">
姓名 (最大 10 个字符): <input type="text" id="fname" size="20"><br>
年龄 (从 1 到 100): <input type="text" id="age" size="20"><br>
E-mail: <input type="text" id="email" size="20"><br>
<br>
<input type="submit" value="提交"> 
</form>
<script>
function myFunction() {
    var at = document.getElementById("email").value.indexOf("@");
    var age = document.getElementById("age").value;
    var fname = document.getElementById("fname").value;
    submitOK = "true";
    if (fname.length>10) {
        alert("姓名不能超过 10 个字符");
        submitOK = "false";
    } 
    if (isNaN(age)||age<1||age>100) {
        alert("年龄范围为 1 到 100");
        submitOK = "false";
    }
    if (at==-1) {
        alert("不合法的 e-mail!");
        submitOK = "false";
    }
    if (submitOK=="false") {
        return false;
    }
}
</script>

</body>
</html>
源代码

动行结果
