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JS基础演示（0224前端学习）
小辰
Original
757 people have browsed it

1.首先效果图

2.下面是我的代码

  1. <!DOCTYPE html>
  2. <html>
  3. <head>
  4.     <meta charset="utf-8">
  5.     <title>js基础演示</title>
  6. </head>
  7. <body>
  8. <li>实例演示变量声明与访问</li>
  9. <li>实例演示变量作用域与访问</li>
  10. <li>实例演示流程控制(分支与循环所有类型)</li>
  11. </body>
  12.     <script>
  13.     // 变量声明与访问
  14.     var q =1314;
  15.     console.log('变量y的值是：' + q);
  16.     // 第二种声明,先定义，然后初始化
  17.     var qa;
  18.     qa=12;
  19.     console.log('变量qa的值是：' + qa);
  20.     // 不在函数申明的变量都默认为全局变量
  21.     //全局变量的访问
  22.     console.log(window);
  23.     console.log(window.qa);
  26.     //变量的作用域与访问
  27.     function hi(){
  28.         var w = 1256;
  29.     }
  30.     //函数外部不能访问函数内部的私有变量
  31.     //console.log(w);
  32.     if (qa=12) {
  33.         var zz = 'zzzzz';
  34.     }
  35.     console.log(zz);
  38.     //流程控制：分支+循环
  39.     //单分支
  40.     var hu = '';
  41.     if (qa <13){
  42.         hu = 'qa这个值小于13';
  43.     }
  44.     console.log(hu);
  46.     //双分支
  47.     var zh ='';
  48.     if (qa<=6){
  49.         zh='这个值小于等于6';
  50.     }else {
  51.         zh='这个值大于6';
  52.     }
  53.     console.log(zh);
  54.     //双分支的简化
  55.     kl =  qa <= 6 ? '值小于6':'值大于6';
  56.     console.log(kl);
  58.     //多分支
  59.     var zh ='';
  60.     if (qa <6) {
  61.         zh='这个值小于6';
  62.     }else if(qa === 6){
  63.         zh='这个值等于6';
  64.     }else if (qa >6){
  65.         zh='这个值大于6';
  66.     }
  67.     console.log(zh);
  68.     //多分支的简化
  69.     var zh ='';
  70.     switch (true){
  71.         case qa<6:
  72.         zh='这个值小于6';
  73.         break;
  74.         case qa===6:
  75.         zh='这个值等于6';
  76.         break;
  77.         default:
  78.         zh='这个值大于6';
  79.         break;
  80.     }
  81.     console.log(zh);
  84.     //循环：for，while
  85.     //for循环
  86.     var sum =1;
  87.     for (var i = 1; i <= 3; i++) {
  88.         sum +=i;
  89.     }
  90.     console.log('累计结果: ' + sum);
  91.     // 对于数组的循环
  92.     var arr = ['123', '456', '789'];
  93.         for (var i = 0; i < arr.length; i++) {
  94.             console.log(arr[i]);
  95.         }
  97.     //while循环
  98.     var sum = 3;
  99.     var i = 0;
  100.     while (i < 10) {
  101.     i++;
  102.     sum += i;     
  103.     }
  104.     console.log('累计结果: ' + sum);
  105.     //do..while
  106.     var sum = 0;
  107.     var i = 0;
  108.     do {
  109.         i++;
  110.         sum += i;
  112.         } while (i > 1) ;
  113.     console.log('累计结果: ' + sum);
  115.     //break和continue的使用
  116.     // break: 终止循环,跳出
  117.     var sum = 0;
  118.     for (var i = 2; i < 6; i++) {
  119.         if (i === 3) break;
  120.         sum += i;
  121.         }
  122.         console.log('累计结果: ' + sum);
  124.     // continue: 终止本次循环, 提前进入下一次
  125.     var sum = 0;
  126.         for (var i = 2; i < 6; i++) {
  127.             if (i === 3) continue;
  128.             sum += i;
  129.         }
  130.         console.log('累计结果: ' + sum);
  131.     </script>
  132. </html>

3.小结
我感觉内容比较简单，还是很容易理解，就是内容有点多，或许是我把它们都写在一起的原因，还有很多作业会慢慢补齐的。

Correcting teacher：天蓬老师天蓬老师

Correction status：qualified

Teacher's comments：觉得简单就会有信心
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