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Home > List of blog posts > javascript变量、函数，流程控制，循环，类型转换作业_2019_12_17
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javascript变量、函数，流程控制，循环，类型转换作业_2019_12_17
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  1. javascript变量、函数的定义

    1. <!DOCTYPE html>
    2. <html lang="en">
    3. <head>
    4.     <meta charset="UTF-8">
    5.     <meta name="viewport" content="width=device-width, initial-scale=1.0">
    6.     <meta http-equiv="X-UA-Compatible" content="ie=edge">
    7.   <title>demo1</title>
    8. </head>
    9. <body>
    10.     <script>
    11. //使用关键字var定义一个变量
    12. ​    var myNum1 = 10;
    13. ​    alert(myNum1);
    14. //使用关键字function定义一个函数
    15. ​    function disPlay(num) {
    16. ​      console.log(num);
    17. ​    }
    18. //调用刚创建的display函数，并传入实参
    19. ​    disPlay(myNum1);
    20.   </script>
    21. </body>
    22. </html>

  1. javascript流程控制if else switch

    1. <!DOCTYPE html>
    2. <html lang="en">
    3. <head>
    4.     <meta charset="UTF-8">
    5.     <title>demo3</title>
    6. </head>
    7. <body>
    8. <script>
    9.     /*
    10.     小明妈妈和小明说：如果你考到90分以上，我就给你买汽车玩具，考到60分到90分之间
    11.     就带你去吃肯德基，如果你考60分以下就回来挨打
    12.      */
    13.     function mamaSay(grade) {
    14.         if(grade>=90){
    15.             alert("买玩具汽车");
    16.         }
    17.         if(grade<90&&grade>=60){
    18.             alert("去吃肯德基");
    19.         }
    20.         if(grade<60){
    21.             alert("回家挨打！");
    22.         }
    23.     }
    24.     function mamaSay2(grade) {
    25.         if (grade >= 90) {
    26.             alert("买玩具汽车");
    27.         } else if (grade < 90 && grade >= 60) {
    28.             alert("去吃肯德基");
    29.         } else {
    30.             alert("回家挨打！");
    31.         }
    32.     }
    33.     function mamaSay3(grade) {
    34.         /*不知为何，我在case中放入表达式会走默认。所以
    35.         我就把grade强制转换为int类型了*/
    36.         grade=parseInt(grade/10);
    37.         switch (grade) {
    38.             case 10:
    39.             case 9:
    40.                 alert("买玩具汽车");
    41.                 break;
    42.             case 8:
    43.             case 7:
    44.             case 6:
    45.                 alert("去吃肯德基");
    46.                 break;
    47.             default:
    48.                 alert("回家挨打！");
    49.         }
    50.     }
    52.     var mygrade = 90;
    53.     mamaSay3(mygrade);
    54. </script>
    55. </body>
    56. </html>

  1. javascript三种循环

    1. <!DOCTYPE html>
    2. <html lang="en">
    3. <head>
    4.     <meta charset="UTF-8">
    5.     <title>demo4</title>
    6. </head>
    7. <body>
    8. <script>
    9.     var arr = [12,15,17,64,84,61,24,56];
    10.     for(i=0;i<arr.length;i++){
    11.         console.log(arr[i]);
    12.     }
    13.     var i = 0;
    14.     while (i<arr.length){
    15.         console.log(arr[i]);
    16.         i++
    17.     }
    18.     i = 0;
    19.     do {
    20.         console.log(arr[i]);
    21.         i++;
    22.     }while (i<arr.length);
    23. </script>
    24. </body>
    25. </html>
  1. 数据类型转换：parseInt、isNaN函数的使用
  1. <!DOCTYPE html>
  2. <html lang="en">
  3. <head>
  4.     <meta charset="UTF-8">
  5.     <title>demo5</title>
  6. </head>
  7. <body>
  8. <script>
  9.     var number = "135";
  10.     number = parseInt(number);
  11.     console.log(number.constructor===Number); //控制台显示ture，转换成功
  13.     var str = "西门大官人";
  14.     console.log(isNaN(number));//控制台显示false，表示变量number是数字，js自动转换为数字了
  15.     console.log(isNaN(str));//控制台显示ture，表示变量str不是数字
  16. </script>
  17. </body>
  18. </html>
Correction status：Uncorrected

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