lovecoding
/
VIP22


			
				
					
						
						
							12345678910111213141516171819202122
							<!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>
    /* 
      变量提升
      通过var 定义的变量  会在当前作用域最上方定义这个变量 但是没有赋值
    */
    console.log(a)
    var a = 10

    console.log(b)//报错
    let b = 20
  </script>
</body>
</html>