js if 判断的使用

!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>同志交友</title>
<style>
input {
width: 300px;
padding: 10px;
font-size: 16px;
border: 1px solid #ccc;
}
button {
padding: 10px 20px;
border: 1px solid #ccc;
background: #f5f5f5;
}
#res {
margin-top:20px;
width: 300px;
min-height: 100px;
padding: 10px;
border:1px solid #ccc;
}

</style>
</head>
<body>
<h1>同志交友</h1>
<hr>
<h3>请输入您的成绩：</h3>
<input type="number" id="score">
<button onclick="makeScore()">提交</button>

<div id="res"></div>

<script>
//声明函数
function makeScore() {
//获取用户输入的成绩
var score = Number(document.getElementById('score').value);

//对成绩进行判断
var resContent = ''; //空字符串 声明定义 变量
if (score >= 90) {
resContent = '不错哦，小同志，很优秀'; //修改变量的值
} else if (score >= 80) {
resContent = '小同志，还行';
} else if (score >= 60) {
resContent = '小同志，及格了';
} else {
resContent = '你不是我的同志';
}

//把结果写入到div中 id=res
document.getElementById('res').innerHTML = resContent;

}

</script>
</body>
</html>