JS Switch

Switch Control Flow

Based on a condition, switch selects one or more code blocks to be executed.

switch executes the code blocks that matches an expression.

switch is often used as a more readable alternative to many if...else if...else statements, especially when dealing with multiple possible values.

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.
• If there is no match, no code is executed.

Example

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";

}

Note: The getDay() method returns the weekday as a number between 0 and 6. (Sunday=0, Monday=1, Tuesday=2 ..)

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.

No more statements in the switch block will be executed.

It is not necessary to break the last case. The switch ends (breaks) there anyway.

Note: The break keyword is crucial for preventing a "fall-through." Without break, the code will continue to execute the next case blocks (and the default block if present) even if their values do not match the expression.

The default Keyword

The default keyword specifies a block of code to run if there is no case match.

The default keyword is optional.

The default can act as a fallback:

Example

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:

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";

  }

Note: 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";

  }

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 uses strict comparison (===).

The values must be of the same type to match.

A strict comparison can only be true if both operands are of the same type.

Example

  let x = "0";
switch (x) {
  case 0:
    text = "Off";

      break;
  case 1:
    text = "On";
    break;

    default:

  text = "No value found";
}