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<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>javascript基础</title>
</head>
<body>
<h2 id="header" style="color: blueviolet" onclick="alert(this.id)">草台班子学习频道</h2>
<h2 id="header" style="color: blueviolet" onclick="alert(id)">草台班子学习频道</h2>
<form action="">
<input name="ban" type="text" value="草台班子">
<button onclick="alert(ban.value)">显示内容</button>
<br>
<input name="username" type="text" placeholder="用户名">
<button onclick="check(username)">验证表单</button>
<script>
function check(username) {
if(username.value.length===0){
alert('用户名空空如也')
}else{
alert('验证通过,您输入的内容是:'+username.value)
}
}
</script>
</form>
</body>
</html>点击 "运行实例" 按钮查看在线实例
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