let const关键字

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>

巴特西

let const关键字

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