let 是取代var
在块级作用域里面有效
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Title</title>
</head>
<body>
<script type="application/javascript">
{
var a=1;
let b=2;
}
console.log(a);
console.log(b);
</script>
</body>
</html>
cons定义常量
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Title</title>
</head>
<body>
<script type="application/javascript">
const a=12;
a=6;
console.log(a);
</script>
</body>
</html>