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<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title></title>
</head>
<body>
<form action="" method="post">
<p>name: <input type="text" id="name"> <span id="name_err"></span></p>
<p>age: <input type="text" id="age"> <span id="age_err"></span></p>
<p>
<button type="button" onclick="myfun()">submit</button>
</p>
</form>
<script>
function myfun() {
name = document.getElementById("name").value;
age = document.getElementById("age").value;
if (name == "") {
document.getElementById("name_err").innerHTML = "請輸入正確的姓名";
}
if (age == "" || isNaN(age)) {
document.getElementById("age_err").innerHTML = "請輸入正確的年齡";
}
}
</script>
</body>
</html>
