js中的for循环，while循环，do...while循环和C语言的一模一样
有几个问题要提醒一下的是
1. null是对象，即object undefined是undefined
demo
1 <!DOCTYPE html>
2 <html>
3 <body>
4
5 <p id="demo"></p>
6
7 <script>
8 document.getElementById("demo").innerHTML =
9 typeof undefined + "<br>" +
10 typeof null + "<br>" +
11 (null === undefined) + "<br>" +
12 (null == undefined);
13 </script>
14
15 </body>
16 </html>
17
结果：
2.几个demo
break的标签引用
1 <!DOCTYPE html>
2 <html>
3 <body>
4
5 <script>
6 cars=["BMW","Volvo","Saab","Ford"];
7 list:
8 {
9 document.write(cars[0] + "<br>");
10 document.write(cars[1] + "<br>");
11 document.write(cars[2] + "<br>");
12 break list;
13 document.write(cars[3] + "<br>");
14 document.write(cars[4] + "<br>");
15 document.write(cars[5] + "<br>");
16 }
17 </script>
18
19 </body>
20 </html>
do-while
1 <!DOCTYPE html>
2 <html lang="en">
3 <head>
4 <meta charset="UTF-8">
5 <title>Document</title>
6 </head>
7 <body>
8 <p>点击下面的按钮，主要i小于5就一直循环代码块</p>
9 <button onclick="myFunction()">hit me</button>
10 <p id="demo"></p>
11 <script>
12 function myFunction()
13 {
14 var x="",i=0;
15 do{
16 x=x+"The number is " +i+ "<br />";
17 i++;
18 }
19 while(i<5)
20 document.getElementById("demo").innerHTML=x;
21
22 }
23 </script>
24
25 </body>
26 </html>
结果：
while
1 <!DOCTYPE html>
2 <html lang="en">
3 <head>
4 <meta charset="UTF-8">
5 <title>Document</title>
6 </head>
7 <body>
8 <p>点击下面的按钮，只要i小于5就一直循环代码块</p>
9 <button onclick="myFunction()">hit me</button>
10 <p id="demo"></p>
11 <script>
12 function myFunction()
13 {
14 var x="",i=0;
15 while(i<5)
16 {
17 x=x+"The number is " +i+ "<br />";
18 i++;
19 }
20 document.getElementById("demo").innerHTML=x;
21 }
22 </script>
23 </body>
24 </html>
结果
：
for
1 <!DOCTYPE html>
2 <html lang="en">
3 <head>
4 <meta charset="UTF-8">
5 <title>Document</title>
6 </head>
7 <body>
8 <script>
9 cars=["BMW","Volvo","Saab","Ford"];
10 var i=0;
11 for(;cars[i];)
12 {
13 document.write(cars[i]+"<br />");
14 i++;
15 }
16 </script>
17 </body>
18 </html>
结果
：
break
1 <!DOCTYPE html>
2 <html lang="en">
3 <head>
4 <meta charset="UTF-8">
5 <title>Document</title>
6 </head>
7 <body>
8 <p>点击按钮，测试带有break语句的循环</p>
9 <button onclick="myFunction()">hit me</button>
10 <p id="demo"></p>
11 <script>
12 function myFunction()
13 {
14 var x="",i=0;
15 for(i=0;i<10;i++)
16 {
17 if(i==3)
18 {
19 break;
20 }
21 x=x+"The numbe is "+i+ "<br />";
22
23 }
24 document.getElementById("demo").innerHTML=x;
25 }
26 </script>
27 </body>
28 </html>
continue
1 <!DOCTYPE html>
2 <html lang="en">
3 <head>
4 <meta charset="UTF-8">
5 <title>Document</title>
6 </head>
7 <body>
8 <p>点击下面的按钮来执行循环，该循环会跳过i=3的步进</p>
9 <button onclick="myFunction()">hit me</button>
10 <p id="demo"></p>
11 <script>
12 function myFunction()
13 {
14 var x="",i=0;
15 for(i=0;i<10;i++)
16 {
17 if(i==3)
18 {
19 continue;
20 }
21 x=x+"the numeber is "+i +"<br />";
22 document.getElementById("demo").innerHTML=x;
23 }
24
25 }
26 </script>
27 </body>
28 </html>
结果：
时间： 2024-10-06 01:53:39