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
<!DOCTYPE html>
<html>
<body> <p id="demo"></p> <script>
document.getElementById("demo").innerHTML =
typeof undefined + "<br>" +
typeof null + "<br>" +
(null === undefined) + "<br>" +
(null == undefined);
</script> </body>
</html>
结果：
2.几个demo
break的标签引用
<!DOCTYPE html>
<html>
<body> <script>
cars=["BMW","Volvo","Saab","Ford"];
list:
{
document.write(cars[0] + "<br>");
document.write(cars[1] + "<br>");
document.write(cars[2] + "<br>");
break list;
document.write(cars[3] + "<br>");
document.write(cars[4] + "<br>");
document.write(cars[5] + "<br>");
}
</script> </body>
</html>
do-while
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Document</title>
</head>
<body>
<p>点击下面的按钮，主要i小于5就一直循环代码块</p>
<button onclick="myFunction()">hit me</button>
<p id="demo"></p>
<script>
function myFunction()
{
var x="",i=0;
do{
x=x+"The number is " +i+ "<br />";
i++;
}
while(i<5)
document.getElementById("demo").innerHTML=x; }
</script> </body>
</html>
结果：
while
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Document</title>
</head>
<body>
<p>点击下面的按钮，只要i小于5就一直循环代码块</p>
<button onclick="myFunction()">hit me</button>
<p id="demo"></p>
<script>
function myFunction()
{
var x="",i=0;
while(i<5)
{
x=x+"The number is " +i+ "<br />";
i++;
}
document.getElementById("demo").innerHTML=x;
}
</script>
</body>
</html>
结果
：
for
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Document</title>
</head>
<body>
<script>
cars=["BMW","Volvo","Saab","Ford"];
var i=0;
for(;cars[i];)
{
document.write(cars[i]+"<br />");
i++;
}
</script>
</body>
</html>
结果
：
break
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Document</title>
</head>
<body>
<p>点击按钮，测试带有break语句的循环</p>
<button onclick="myFunction()">hit me</button>
<p id="demo"></p>
<script>
function myFunction()
{
var x="",i=0;
for(i=0;i<10;i++)
{
if(i==3)
{
break;
}
x=x+"The numbe is "+i+ "<br />"; }
document.getElementById("demo").innerHTML=x;
}
</script>
</body>
</html>
continue
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Document</title>
</head>
<body>
<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>
<button onclick="myFunction()">hit me</button>
<p id="demo"></p>
<script>
function myFunction()
{
var x="",i=0;
for(i=0;i<10;i++)
{
if(i==3)
{
continue;
}
x=x+"the numeber is "+i +"<br />";
document.getElementById("demo").innerHTML=x;
} }
</script>
</body>
</html>
结果：
