JavaScript
Switch Statement
The switch
statement is used to perform different actions based on different conditions.
The
JavaScript Switch Statement
Use the
switch statement to select one of many blocks of code to be executed.
Syntax
switch(expression)
{
case n:
code block
break;
case n:
code block
break;
default:
code block
}
This is how
it works:
The switch
expression is evaluated once.
The value of
the expression is compared with the values of each case.
If there is
a match, the associated block of code is executed.
Example
The getDay()
method returns the weekday as a number between 0 and 6.
(Sunday=0,
Monday=1, Tuesday=2 ..)
This example
uses the weekday number to calculate the weekday name:
switch
(new Date().getDay()) {
case 0:
day = "Sunday";
break;
case 1:
day = "Monday";
break;
case 2:
day = "Tuesday";
break;
case 3:
day = "Wednesday";
break;
case 4:
day = "Thursday";
break;
case 5:
day = "Friday";
break;
case 6:
day = "Saturday";
}
The result
of day will be:
Tuesday
»
The break
Keyword
When
JavaScript reaches a break keyword, it breaks out of the switch block.
This will
stop the execution of more code and case testing inside the block.
When a match
is found, and the job is done, it's time for a break. There is no need for more
testing.
A break can
save a lot of execution time because it "ignores" the execution of
all the rest of the code in the switch block.
It is not
necessary to break the last case in a switch block. The block breaks (ends)
there anyway.
The default
Keyword
The default
keyword specifies the code to run if there is no case match:
Example
The getDay()
method returns the weekday as a number between 0 and 6.
If today is
neither Saturday (6) nor Sunday (0), write a default message:
switch
(new Date().getDay()) {
case 6:
text = "Today is Saturday";
break;
case 0:
text = "Today is Sunday";
break;
default:
text = "Looking forward to the
Weekend";
}
The result
of text will be:
Looking
forward to the Weekend
»
The default
case does not have to be the last case in a switch block:
Example
switch
(new Date().getDay()) {
default:
text = "Looking forward to the
Weekend";
break;
case 6:
text = "Today is Saturday";
break;
case 0:
text = "Today is Sunday";
}
»
If default
is not the last case in the switch block, remember to end the default case with
a break.
Common Code
Blocks
Sometimes
you will want different switch cases to use the same code.
In this
example case 4 and 5 share the same code block, and 0 and 6 share another code
block:
Example
switch
(new Date().getDay()) {
case 4:
case 5:
text = "Soon it is Weekend";
break;
case 0:
case 6:
text = "It is Weekend";
break;
default:
text = "Looking forward to the
Weekend";
}
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