switch (expression){
     case value :statement1
         break;
     case value2 :statement2
         break;
     ....
         case value: statement
         break;
     default :statement;

    iwork = parseInt(prompt("請輸入1-5的值"));
     switch (iwork) {
         case 1 :document.write("星期一")
             break;
         case 2 : "星期2"
             break;
         case 3 : "星期3"
             break;
         case 4 : "星期4"
             break;
         case 5 : "星期5"
             break;
         default :"要輸入合理值";