The JavaScript switch statement is used to execute one code from multiple expressions.
A typical switch statement is
- the first
switch, followed by an expression which is often referred to as the control expression or control variable of the switch statement - subsequent lines defining the actual cases (the values), with corresponding sequences of statements for execution when a match occurs
- a
breakstatement typically follows acasestatement to end said statement.
Each alternative begins with the particular value, or list of values , that the control variable may match and which will cause the control to goto the corresponding sequence of statements. The value (or list/range of values) is usually separated from the corresponding statement sequence by a colon. Every case must also be preceded by a keyword such as case.
An optional default case is typically also allowed, specified by a defaultkeyword. This executes when none of the other cases match the control expression.
syntax
switch(expression to be tested)
{
case value1:
code to be executed if a match;
break;
case value2:
code to be executed if a match;
break;
default:
code to be executed if above values are not matched;
}
Examples
This example has a preset value
<html>
<body>
<script>
var grade='A';
var result;
switch(grade)
{
case 'A':
result="A Grade";
break;
case 'B':
result="B Grade";
break;
case 'C':
result="C Grade";
break;
default:
result="No Grade";
}
document.write(result);
</script>
</body>
</html>
This example displays the day by using the getDay() method which returns the weekday as a number between 0 and 6.
<!DOCTYPE html>
<html>
<body>
<script>
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";
}
document.write(day);
</script>
</body>
</html>
The break Keyword
When JavaScript reaches a break keyword, it breaks out of the switch block. This will stop the execution inside the switch block.
It is not necessary to break the last case in a switch block.
If you omit the break statement, the next case will be executed even if the evaluation does not match the case. This can be a common programming error. Modify the above code example and run this and see what happens, especially on Sunday
<!DOCTYPE html>
<html>
<body>
switch (new Date().getDay())
{
case 0:
day = "Sunday";
case 1:
day = "Monday";
case 2:
day = "Tuesday";
case 3:
day = "Wednesday";
case 4:
day = "Thursday";
case 5:
day = "Friday";
case 6:
day = "Saturday";
}
document.write(day);
</script>
</body>
</html>
The default Keyword
The default keyword specifies the code to run if there is no case match:
In this example if its not Saturday or Sunday the default will be printed which is Work day – sorry
<!DOCTYPE html>
<html>
<body>
<script>
switch (new Date().getDay())
{
case 6:
day = "It is Saturday";
break;
case 0:
day = "It is Sunday";
break;
default:
day = "Work day - sorry";
}
document.write(day);
</script>
</body>
</html>