12.JS的基本语法.html

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>JS的基本语法</title>
</head>
<body>
    <script>
        var x;      //具有函数作用域,少用
        let y = 5;  //具有块级作用域,多使用
        const PI = 3.14;//常量,多使用
        console.log(x,y,PI)
        let name = 'ddh';
        console.log(name);
        let empty = null;
        console.log(empty)
        let age = 18
        if(age > 18){
            console.log('你已经成年')
        }
        else{
            console.log('你未成年')
        }
        for(let i=1;i<11;i++)
        {
           
            if(i == 2){
                continue
            }
            else if(i == 4){
                break
            }
            console.log(i)
        }
        
    </script>
</body>
</html>