实例演示四种常用的函数类型

<script>
      // 命名函数
      let r = 8;
      const PI = 3.14;
      console.log(square(r));
      function square(radio) {
        return (
          `命名函数计算半径为${radio}cm 的圆形面积为 ` +
          PI * radio * radio +
          ` cm^2`
        );
      }
      // 匿名函数
      let square1 = function (r) {
        return `匿名函数计算半径为${r}cm 的圆形面积为 ` + PI * r * r + ` cm^2`;
      };
      console.log(square1(5));
      // 箭头函数
      let square2 = (r) => {
        return `箭头函数计算半径为${r}cm 的圆形面积为 ` + PI * r * r + ` cm^2`;
      };
      console.log(square2(9));
      // 立即执行函数
      let square3 = (function () {
        return (
          `立即执行函数计算半径为${r}cm 的圆形面积为 ` + PI * r * r + ` cm^2`
        );
      })(12);
      console.log(square3);
    </script>

实际演示原始数据类型与引用类型

      let uname = "mike";
      let age = 28;
      let gender = null;
      let mail;
      let student = [uname, age, gender, mail];
      console.table(student);
      let workmate = { name: uname, age: age, gender: gender, mail: mail };
      console.dir(workmate);
      let ismale = workmate.gender == "male";
      console.log(
        workmate.name +
          "'s age is " +
          workmate["age"] +
          ". gender is male? " +
          ismale
      );

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