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：
