js基础

<!DOCTYPE html>
<html lang="zh-CN">
<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>js演示</title>
</head>
<body>
    <script>  
    // 声明变量 a,且初始化赋值
    let a =10;
    let b =20;
    console.log( a);
    console.log(b);
    // 匿名函数
    {
    a + b ;
      let c =1;
      c =  a + b ;
      console.log(c);
      console.log(typeof(a + b ));
      let d = '朱老师' ;
      console.log( d);
      console.log( typeof (d));
      console.log(typeof(d +c));
    }
    // console.log(c);    块的  作用域原因不能访问
    // {
    //     // 在js中, 字符串的拼装: "+",二边至少有一个字符串
    //     let s = 'Hello ' + 'World';
    //     console.log(s);
    //     console.log('a=', a, ', b=', b);
    //     console.log(a + b);
    //     console.log(a + '10');
    //     console.log(typeof (a + '10'));
    //   }
// 命名函数
   function sum ( a,b  ){
   return  a  +  b ;
   }
     console.log(sum(10 , ',朱老师' ));
   console.log(sum(1, 2 ));
   function sum (j  , k ) {
   let e = j+ k ;
    return e ;
   }
 console.log(sum (11, 20));
// 全局作用域
let email = '123@qq.com';
{
    console.log(email);
}
let email2 = '456@qq.com' ;
   {
    let email2 = ' 789@qq.com';
    console.log(email2);
}
console.log(email2);
// 我是常量
const H = 66  ;
console.log(H);
//变量 命名法
// 1、驼峰    大驼峰  UserName   小驼峰  userName   动词+名词
// 2、蛇形     user_name
//常量 命名法
// USERNAME
// 命名函数
 function getName(userName){
  return  'hello,' +userName ;
 }
 console.log( getName('朱老师'));
//  匿名函数
let getName1 = function (userName1){
 return 'hello' + userName1 ;
}
 console.log(getName1('灭绝老师'));
      // let getUserName = function (username) {
      //   return 'Hello, ' + username;
      // };
      // console.log(getUserName('马老师'));
      // console.log(getUserName('牛老师'));
      // console.log(getUserName('羊老师'));
  //     console.log(lhusername)(
  // function (lhusername) {
  //   return 'hello,' + lhusername ;
  // }
  //     );
// 阅读及焚
      console.log(
        (function (qjusername) {
          return 'Hello, ' + qjusername;
        })('灭绝老师')
      )  ;
// 简化匿名函数
// 去掉 function  及形参的括弧，在形参的右侧增加 =>  胖箭头  
getName1 = userName1 =>  {
 return 'hello,' + userName1 ;
}
 console.log(getName1('go老师'));
// 再次简化 ，去掉{   }   ，去掉return 注意又有分号
getName1 = userName1 =>  
'hello,' + userName1 ;
 console.log(getName1('猫老师'));
let f = x  => x * 2  ;
console.log(f (3));
f =(x ,z) => 5*7 ;
console.log(f());
f =(x ,z) => x+ z ;
console.log(f(4,9));
f =() => 'hello ,桌面花纹'
console.log(f());
    </script>
</body>
</html>

Correcting teacher：

PHPz

Correction status：qualified

Teacher's comments：

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js基础