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javascript数据类型和分支循环
秋闲独醉
Original
232 people have browsed it
  2. <!DOCTYPE html>
  3. <html lang="en">
  4.   <head>
  5.     <meta charset="UTF-8" />
  6.     <meta http-equiv="X-UA-Compatible" content="IE=edge" />
  7.     <meta name="viewport" content="width=device-width, initial-scale=1.0" />
  8.     <title>javascript数据类型和分支循环</title>
  9.   </head>
  10.   <body>
  11.     <script>
  12.       //   javascript数据类型分为
  13.       //   1、原始类型： Number String Boolean undefined null
  14.       //   2、引用类型：array object function
  15.       // number
  16.       console.log("这是number:" + 123);
  17.       //string
  18.       console.log("这是string:" + "123");
  19.       //boolean
  20.       console.log("这是boolean:" + false);
  21.       //undefined
  22.       let a;
  23.       console.log("这是undefined:" + a);
  24.       //null
  25.       let b = null;
  26.       console.log("这是null:" + b);
  27.       //array
  28.       let arr = ["小明", "男", "16", "16cm"];
  29.       console.log("这是array:" + arr);
  30.       let obj1 = [
  31.         { name: "手机", num: 2, price: 5000 },
  32.         { name: "电脑", num: 5, price: 6000 },
  33.         { name: "相机", num: 4, price: 2000 },
  34.       ];
  35.       console.log("这是array:" + obj1[0].name);
  36.       //object
  37.       let obj = {
  38.         name: "Tom",
  39.         age: 18,
  40.         height: "180cm",
  41.         fun: function () {
  42.           console.log("这是一个function.");
  43.         },
  44.       };
  45.       console.log("这是一个object:" + obj["age"]);
  46.       console.log("这是一个object:" + obj.age);
  47.       obj.fun();
  49.       //查看数据类型用typeof
  50.       console.log(typeof function () {});
  51.       console.log(arr instanceof Object);
  53.       //回调函数
  54.       function f1() {}
  55.       function f2(f1) {
  56.         console.log("这是回调函数" + typeof f1);
  57.       }
  58.       f2(f1);
  59.       //这是闭包函数
  60.       function f3() {
  61.         return function () {
  62.           return "hello world";
  63.         };
  64.       }
  65.       console.log("这是闭包函数" + f3()());
  66.     </script>
  67.     <script>
  68.       //分支和循环
  69.       // 1、单分支
  70.       if (true) {
  71.         console.log("这是一个单分支");
  72.       }
  73.       //2、双分支
  74.       if (false) {
  75.         console.log("这个是双分支,真的");
  76.       } else {
  77.         console.log("这个是双分支,假的");
  78.       }
  80.       //3、三元运算
  81.       let res;
  82.       isNaN(123) ? (res = "是") : (res = "不是");
  83.       console.log("这" + res + "三元运算");
  85.       //多分支
  86.       let age = 20;
  87.       if (age < 18) {
  88.         console.log("年龄小于18岁");
  89.       } else if (age >= 18 && age < 25) {
  90.         console.log("正是青春年华");
  91.       } else if (age >= 25) {
  92.         console.log("差不多了");
  93.       }
  94.       //switch判断分支
  95.       //必须要用true做为switch入口判断条件
  96.       switch (true) {
  97.         case age < 18:
  98.           console.log("年龄小于18岁");
  99.           breack;
  100.         case age >= 18 && age < 25: {
  101.           console.log("正是青春年华");
  102.           break;
  103.         }
  104.         default: {
  105.           console.log("差不多了");
  106.         }
  107.       }
  108.       //for循环，for of 循环 ，for in 循环
  109.       arr = [9, 4, 2, 7, 4];
  110.       obj = {
  111.         product: "电视",
  112.         num: 3,
  113.         price: 300,
  114.         fun: function () {},
  115.       };
  117.       //for循环
  118.       for (let i = 0; i < arr.length; i++) {
  119.         console.log("for循环:" + arr[i]);
  120.       }
  121.       //for of 循环
  122.       for (let item of arr) {
  123.         console.log("for of循环:" + item);
  124.       }
  125.       for (let item of arr.values()) {
  126.         console.log("for of循环值:" + item);
  127.       }
  128.       for (let item of arr.keys()) {
  129.         console.log("for of循环键:" + item);
  130.       }
  132.       //for in 循环
  133.       for (let key in obj) {
  134.         console.log("for in循环键:" + key);
  135.       }
  136.       //这里只能发obj[key]访问，不能用obj.key .obj[key],key不能有引号
  137.       for (let key in obj) {
  138.         console.log("for in循环值:" + obj[key]);
  139.       }
  140.     </script>
  141.   </body>
  142. </html>
Correcting teacher：PHPzPHPz

Correction status：qualified

Teacher's comments：
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