Under Certain Conditions - JavaScript by Example - page 130

EXAMPLE 6.4 ( CONTINUED )

<script type="text/javascript">
<!--

1 var day_of_week=Math.floor((Math.random()* 7)+1);

// Get a random number between 1 and 7
// Monday is 1, Tuesday is 2, etc.

2 switch(day_of_week){

3 case 1:

case 2:
case 3:
case 4:

4 alert("Business hours Monday through Thursday are from

9am to 10pm");

5 break;

case 5:
alert("Business hours on Friday are from 9am to 6pm");
break;
case 6:
alert("Business hours on Saturday are from
11am to 3pm");

break;

6 default:

alert("We are closed on Sundays and holidays");

7 break;

8 }

//-->
</script>
</body>
</html>

EXPLANATION
1 The random number function generates a random number between 1 and 7 inclu-

sive when the script is executed. The random number is stored in a variable called
day_of_week .

2 The day_of_week value of the switch expression is matched against the values of

each of the case labels below.

3 The first case that is tested is 1 . If the random number is 1, the message “ Business

hours Monday through Thursday are from 9am to 10pm ” will be displayed in the
alert dialog box. The same is true for case 2, 3, and 4.

4 This statement is executed if case 1, 2, 3, or 4 are matched. Note there are no break

statements associated with any of these 4 case statements. Program control just
drops from one case to the next, and if cases 1, 2, 3, or 4 are not matched, execu-
tion control goes to the next case (case 5) for testing.

5 The break statement causes program control to continue after line 8. Without it,

the program would continue executing statements into the next case , “yellow” ,
and continue doing so until a break is reached or the switch ends—and we don't
want that. The break statement sends control of the program to line 8.