js中with的和case的用法

switch Statement

Enables the execution of one or more statements when a specified expression's value matches a label.



switch (expression) {

   case label :

       statementlist

   case label :

       statementlist

   ...

   default :

       statementlist

}



Arguments

expression



The expression to be evaluated.



label



An identifier to be matched against expression. If label === expression, execution starts with the statementlist immediately after the colon, and continues until it encounters either a break statement, which is optional, or the end of the switch statement.



statementlist



One or more statements to be executed.



Remarks

Use the default clause to provide a statement to be executed if none of the label values matches expression. It can appear anywhere within the switch code block.



Zero or more label blocks may be specified. If no label matches the value of expression, and a default case is not supplied, no statements are executed.



Execution flows through a switch statement as follows:



Evaluate expression and look at label in order until a match is found.

If a label value equals expression, execute its accompanying statementlist.

Continue execution until a break statement is encountered, or the switch statement ends. This means that multiple label blocks are executed if a break statement is not used.