switch

JavaScript

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JavaScript手册

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? ");

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