JavaScript Switch Case

You can use multiple if...else…if statements, as in the previous chapter, to perform a multiway branch. However, this is not always the best solution, especially when all of the branches depend on the value of a single variable.

Starting with JavaScript 1.2, you can use a switch statement which handles exactly this situation, and it does so more efficiently than repeated if...else if statements.

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

Syntax

switch(expression) {
  case x:
    // code block
    break;
  case y:
    // 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

 

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:

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 the 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.

 

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 shares 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";
}

 

Switching Details

If multiple cases match 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.

In this example there will be no match for x:

Example

var x = "0";
switch (x) {
  case 0:
    text = "Off";
    break;
  case 1:
    text = "On";
    break;
  default:
    text = "No value found";
}