为社么不行
<!DOCTYPE html>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>prompt</title>
<script type="text/javascript">
function contxt(){
var num=prompt("请输入你的成绩:") ;
if (num>=90)
{
document.write("很棒");
}
else(num>=75)
{
document.write("不错");
}
else(num>=60)
{
document.write("加油");
}
else
{
document.write("努力");
}
}
</script>
</head>
<body>
<button onclick="contxt()"> 点击 </button>
</body>
</html>
