
JavaScript手册
	目录
	此参考中包含的内容
	轻松上手
	简介
	操作符
	语句
	核心
	文档
	窗口
	表单
	浏览器
	事件和事件句柄
	LiveWire 数据库服务
	进程管理服务
	实用工具
	全局函数
	LiveConnect 的Java包
	索引
	版权

switch

Allows a program to evaluate an expression and attempt to match the expression's value to a case label.

实现版本 Navigator 4.0, Netscape Server 3.0

语法

switch (expression){
   case label :
      statement;
      break;
   case label :
      statement;
      break;
   ...
   default : statement;
}

参数

expression Value matched against label.
label Identifier used to match against expression.
statement Any statement.

描述

If a match is found, the program executes the associated statement.

The program first looks for a label matching the value of expression and then executes the associated statement. If no matching label is found, the program looks for the optional default statement, and if found, executes the associated statement. If no default statement is found, the program continues execution at the statement following the end of switch.

The optional break statement associated with each case label ensures that the program breaks out of switch once the matched statement is executed and continues execution at the statement following switch. If break is omitted, the program continues execution at the next statement in the switch statement.

示例

In the following example, if expression evaluates to "Bananas," the program matches the value with case "Bananas" and executes the associated statement. When break is encountered, the program breaks out of switch and executes the statement following switch. If break were omitted, the statement for case "Cherries" would also be executed.

switch (i) {
 case "Oranges" :
 document.write("Oranges are $0.59 a pound. ");
 break;
 case "Apples" :
 document.write("Apples are $0.32 a pound. ");
 break;
 case "Bananas" :
 document.write("Bananas are $0.48 a pound. ");
 break;
 case "Cherries" :
 document.write("Cherries are $3.00 a pound. ");
 break;
 default :
 document.write("Sorry, we are out of " + i + ". ");
}
document.write("Is there anything else you'd like? ");

回页面顶部