JavaScript学习进度 

 1 <!DOCTYPE html>
 2 <html>
 3     <head>
 4         <meta charset="utf-8" />
 5         <meta name="viewport" content="width=device-width, initial-scale=1">
 6         <title>1</title>
 7     </head>
 8     <body>
 9 您可以在字符串中使用引号，只要不匹配包围字符串的引号即可： 
10 <script type="text/javascript">
11 var carname = "Volvo XC60";
12 var carname = 'Volvo XC60';
13 var answer1 = 'It\'s alright';
14 var answer2 = "He is called \"Johnny\"";
15 var answer3 = 'He is called"Johny"';
16 document.write(carname1 + "<br>")
17 document.write(carname2 + "<br>")
18 document.write(answer1 + "<br>")
19 document.write(answer2 + "<br>")
20 document.write(answer3 + "<br>")
21              
22         </script>
23  -->
24 极大或极小的数字可以通过科学（指数）计数法来书写：
25 <script type="text/javascript">
26 var x1 = 34.00;
27 var x2 = 34;
28 var y = 123e5;
29 var z = 123e-5;
30 document.write(x1 + "<br>")
31 document.write(x2 + "<br>")
32 document.write(y + "<br>")
33 document.write(z + "<br>")
34 </script>
35 
36 下面的代码创建名为 cars 的数组：
37 <script type="text/javascript">
38     var i;
39     var cars = new Array();
40     cars[0] = "Saab";
41     cars[1] = "Volvo";
42     cars[2] = "BMW";
43     
44     for (i =0; i<cars.length; i++)
45     {
46     document.write(cars[i] + "<br>");
47     }
48 </script>
49  
50 对象属性有两种寻址方式：
51 <script type="text/javascript">
52 var person = 
53 {
54     firstname : "John",
55     lastname : "Doe",
56     id           : 5566
57 };
58 document.write(person.lastname + "<br>");
59 document.write(person["lastname"] + "<br>"); 
60 </script>
61  Undefined 这个值表示变量不含有值。
62 
63 可以通过将变量的值设置为 null 来清空变量。
64 <script type="text/javascript">
65 var person;
66 var car = "Volvo";
67 document.write(person + "<br>");
68 document.write(car + "<br>");
69 var car = null
70 document.write(car + "<br>");
71 </script>
72 
73 </body>
74 </html>

 

posted @ 2020-08-11 12:29  GMH关  阅读(96)  评论(0)    收藏  举报