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1. 变量,常量,数据类型,实例演示,注意命名规范;

js的变量和常量，变量可更新，可先声明再赋值，常量不可更新，声明时必须初始化，变量声明用let,常量声明用const

<!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>编程常识之变量、常量</title>
  </head>
  <body>
    <script>
      // 最重要的两类成员：函数和数据
      // 传统的变量方式，已淘汰或不建议使用
      //   var email = "a@qq.com";
      //   document.write(email);
      //   alert(email);
      //   var email = "555@qq.com";
      //   console.log(email);
      //   console.info(email);
      //   传统js,es6之前的js没有常量，靠自觉靠约定
      //   var APP_NAME = "在线商城";
      //   var APP_NAME = "我的小程序";
      //   console.log(APP_NAME);
      let email = "222@qq.com";
      //   let email = "333@qq.com";
      console.log(email);
      // 常量不能被更新，声明时必须初始化
      const NATION = "China";
      console.log(NATION);
    </script>
  </body>
</html>

效果图如下

js的数据类型包括原始类型和引用类型

1、原始类型包括
数值：整数，小数
字符串：使用双引或者单引号
undefined:未定义
null:空
2、引用类型/对象

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width= , initial-scale=1.0" />
    <title>数据类型</title>
  </head>
  <body>
    <script>
      //   1.原始
      //   2.引用
      function hello() {}
      console.log(typeof hello);
      console.dir(hello);
    </script>
  </body>
</html>

效果如下

2. 函数参数与返回值,匿名函数及箭头函数的转化,实例演示;

<!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>
      function aa() {
        return 3 + 4;
      }
      console.log(aa());
      function bb(a, b) {
        return a + b;
      }
      console.log(bb(4, 4));
      //   匿名函数
      let nimi = function () {
        return 5 + 4;
      };
      console.log(nimi());
      //   匿名函数改造为箭头函数
      let nimi1 = () => 5 + 4;
      console.log(nimi1());
    </script>
  </body>
</html>

运行效果如下

Correcting teacher：

天蓬老师

Correction status：qualified

Teacher's comments：

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1. 变量,常量,数据类型,实例演示,注意命名规范;

js的变量和常量，变量可更新，可先声明再赋值，常量不可更新，声明时必须初始化，变量声明用let,常量声明用const

效果图如下

js的数据类型包括原始类型和引用类型

2. 函数参数与返回值,匿名函数及箭头函数的转化,实例演示;