switch 可以省略default的break

var day=new Date().getDay();
switch (day)
{
case 6:
x="Today it's Saturday";
break;
case 0:
x="Today it's Sunday";
break;
default:
x="Looking forward to the Weekend";
}

循环分为以下几种
for

for (var i=0; i<5; i++)
{
x=x + "The number is " + i + "<br>";
}

可以省略初赋值

var i=2,len=cars.length;
for (; i<len; i++)
{
document.write(cars[i] + "<br>");
}

遍历对象

var person={fname:"John",lname:"Doe",age:25};

for (x in person)
  {
  txt=txt + person[x];
  }

break 搭配标签引用可以跳出任何JS代码块

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>");
}

try-catch-throw
```
<!DOCTYPE html>
<html>
<body>
```

我的第一个 JavaScript 程序

请输入 5 到 10 之间的数字：

```