JavaScript Switch Statement
Switch Statement
The switch statement is used to perform different actions based on different conditions.Use the switch statement to select one of many code blocks to be executed.
switch(expression) {
case x:
// code block
break;
case y:
// code block
break;
default:
// code block
}
- 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.
- If there is no match, the default code block is executed.
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 break Keyword
When JavaScript reaches a break keyword, it breaks out of the switch block.
This will stop the execution of inside the block.It is not necessary to break the last case in a switch block. The block breaks (ends) there anyway.
Note: If you omit the break statement, the next case will be executed even if the evaluation does not match the case.
The default Keyword
The default keyword specifies the code to run if there is no case match.The default case does not have to be the last case in a switch block:
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 default case does not have to be the last case in a switch block. If default is not the last case in the switch block, remember to end the default case with a break.
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";
}
Common Code Blocks
Sometimes you will want different switch cases to use the same code.
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";
}
Switching Details
If multiple cases matches a case value, the first case is selected. If no matching cases are found, the program continues to the default label.
If no default label is found, the program continues to the statement(s) after the switch.
Strict Comparison
Switch cases use strict comparison (===). The values must be of the same type to match. A strict comparison can only be true if the operands are of the same type.
var x = "0";
switch (x) {
case 0:
text = "Off";
break;
case 1:
text = "On";
break;
default:
text = "No value found";
}
Declaring (Creating) JavaScript Variables
Creating a variable in JavaScript is called "declaring" a variable. You declare a JavaScript variable with the var keyword: var carName;
After the declaration, the variable has no value (technically it has the value of undefined). To assign a value to the variable, use the equal sign:
carName = "Volvo";
It's a good programming practice to declare all variables at the beginning of a script.
var carName = "Volvo";
document.getElementById("demo").innerHTML = carName;
