document.write("Hello JS")
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8" />
<title></title>
<script>
function callalert()
{
alert('我被点了一下');
}
</script>
</head>
<body>
<button onclick="alert('我被点了')">点我</button>
<button onclick="callalert()">点我一下</button>
<script>
//alert("Hi!");
</script>
</body>
</html>