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The switch statement provides the user with several options and
returns a result based upon the user's selection. It resembles the if/else
statement but is more manageable and efficient. The switch statement
doesn't need to do a comparison for each option. It merely looks for a match
with the expression and executes the code within the case statement.
There is only one set of curly brackets. Formatting the code, as shown below,
makes reading (and debugging) easier. The style of the format is optional; however,
it makes good programming sense to choose some type formatting to help eliminate
errors. The format we will use is:
switch(expression) {
case option1:
statement;
break;
case option2:
statement;
break;
case option3:
statement;
break;
default:
statement;
break;
}
Basically, the switch statement compares the expression in the
parentheses with the option listed in each case statement. When
it finds one that matches, it carries out the instructions given in the case
statement. Usually each case statement ends with a break or a return
command. That way, if the condition is true, the switch statement
will stop executing and return to the main script. Otherwise, each case
statement after the one that matches the parameters would be executed. The switch
statement can also end with a default statement, which would give
a value without being compared to the expression. If there is no default
statement, and a match cannot be found within the case options,
execution will return to the main script. Here's an example of a switch
statement:
var theName="Fred";
switch (theName) {
case "George" :
alert("George is an OK name");
break;
case "Fred" :
alert("Fred is the coolest name!");
alert ("Hi there, Fred");
break;
default :
alert(theName + " is an interesting name you have there.");
break;
}
This is one based on the if/else statement we made previously.
In this one, the switch statement is using the Boolean term true
to determine the value of the case statement. Here's what is happening
when the script is executed:
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Let's take a look at a script we wrote earlier
in this installment. We had used else/if statements for that script.
This time we'll use a switch statement:
function meeting() {
var text = "The meeting this week will be at ";
var nowDate = new Date();
var currDate = nowDate.getDate();
switch(true) {
case (currDate < 5) && (currDate > 0):
document.write(text + "Steve's house");
break;
case (currDate < 12) && (currDate > 4):
document.write(text + "Nancy's house");
break;
case (currDate < 19) && (currDate > 11):
document.write(text + "Mike's house");
break;
default:
document.write(text + "Sally's house");
break;
}
}
This script accomplishes the same thing as our previous one but in a different
manner. Everything is the same up to the switch statement. This
is where the change occurs but it's not all that different. When the script
finds a case statement that is true, as given in the switch
statement, it will execute the statement and then stop. As I said, this is the
same as the else/if statement we presented earlier only it's a
little easier to understand. Let's take a look at another one:
var yourGrade=prompt("Enter the student's grade","Use CAPITALS");
switch(yourGrade) {
case 'A':
alert("Excellent");
break;
case 'B':
alert("Good");
break;
case 'C':
alert("OK");
break;
case 'D':
alert("Mmmmm....");
break;
case 'F':
alert("You must do better than this");
break;
default:
alert("You need to enter either A, B, C, D, or F");
break;
}
You can add additional case statements to allow for further conditions in order to obtain the same result. For instance, if you wanted to allow for upper and lower case letters in the script above, you could format each case statement as follows:
case 'A':
case 'a':
alert("Excellent");
break;
You can also use values in switch statements, as shown below:
var n=prompt("Enter a number between 1 to 3:",0);
switch(n) {
case(n="1"):
alert("You typed "+n);
break;
case(n="2"):
alert("You typed "+n);
break;
case(n="3"):
alert("You typed "+n);
break;
default:
alert("Wrong number");
break;
}
Modifying our previous script using the date, we could use the switch
statement to obtain the date of the week using the getDay object
instead of the getDate:
var dat = new Date()
today=dat.getDay()
switch (today) {
case 0:
document.write("Today is Sunday")
break
case 1:
document.write("Today is Monday")
break
case 2:
document.write("Today is Tuesday")
break
case 3:
document.write("Today is Wednesday")
break
case 4:
document.write("Today is Thursday")
break
case 5:
document.write("Today is Friday")
break
case 6:
document.write("Today is Saturday")
break
}
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Created: June 10, 2005
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