JS Switch

JavaScript Switch Statement

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The switch statement is used to perform different actions based on different conditions.

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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:

Saturday

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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.

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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:

Today is Saturday

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.

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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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