<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Document</title>
</head>
<body>
<script>
let a = 123;
const ABC = "常量";
ABC = 1;
console.log(a); //可以改变的量是变量。
console.log(ABC); //常量不能改变的量是常量。
</script>
</body>
</html>