<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>严格模式</title>
</head>
<body>
<script>
//js存在严格格式
//开启严格模式
'use strict'
var username = '小丽丽';
//userage = 100; //严格模式下 声明变量必须加 var
console.log(username)
</script>
</body>
</html>