Introduction to JavaScript Switch Cases

Introduction to JavaScript Switch Cases

Bolaji Ayodeji's photo
Bolaji Ayodeji
·

4 min read

In this short article, I will introduce you to JavaScript switch cases and how to use them with practical examples. PS: This article is not for those without any JavaScript knowledge; it is expected that you're taking some tutorial or course and you just got to the switch cases section. This article will explain better with more practical examples to help you understand switch cases in depth.

Prerequisites.

  • Basic JavaScript knowledge
  • Code editor
  • Web Browser
  • Your brain :)

The Switch Syntax

A switch statement can basically replace multiple if checks in JavaScript. It gives a more descriptive way to compare a value with multiple variants.

The switch has one or more case blocks and an optional default case.

switch(x) {
  case 'value1':  // if (x === 'value1')
    //code here
    [break]

  case 'value2':  // if (x === 'value2')
    //code here
    [break]

  default:
    //code here
    [break]
}
  • The value of x is checked for strict equality to the value from the first case (that is, value1) then to the second (value2) and so on.
  • If the equality is found, switch starts to execute the code starting from the corresponding case, until the nearest break(or until the end of switch).
  • If no case is matched then the default code is executed (if it exists).

Some few real examples

  • Simple Play & Pause Switch

The switch statement can be used for multiple branches based on a number or string:

switch (movie) {
  case 'play':
    playMovie();
    break;
  case 'pause':
    pauseMovie();
    break;
  default:
    doNothing();
}

If you don’t add a break statement, the execution will "fall through" to the next level. It's essential that you deliberately label the fall through with a comment if you really meant it to aid debugging:

switch (movie) {
  case 'play': // fallthrough
  case 'pause':
    pauseMovie();
    break;
  default:
    doNothing();
}

The default clause is optional. You can have expressions in both the switch part and the cases if you like; comparisons take place between the two using the === operator:

switch (3 + 7) {
  case 5 + 5:
    correct();
    break;
  default:
    neverhappens();
}
  • Simple Maths Calc Switch
let average = 2 + 6;

switch (average) {
  case 4:
    alert( 'Too small' );
    break;
  case 8:
    alert( 'Exactly!' );
    break;
  case 10:
    alert( 'Too large' );
    break;
  default:
    alert( "Incorrect values!" );
}

Here the switch starts to compare average from the first case variant, that is 4. The match fails.

Then 8. That’s a match, so the execution starts from case 8 until the nearest break.

If there is no break, then the execution continues with the next case without any checks.

Here is an example without break:

let average = 2 + 6;

switch (average) {
  case 4:
    alert( 'Too small' );
  case 8:
    alert( 'Exactly!' );
  case 10:
    alert( 'Too big' );
  default:
    alert( "Incorrect values!" );
}

In the example above, we’ll see the sequential execution of three alerts:

alert( 'Exactly!' );
alert( 'Too big' );
alert( "Incorrect values!" );
  • getDay() method switch case

The getDay() method returns the weekday as a number between 0 and 6.

(Sunday=0, Monday=1, Tuesday=2 , Wednesday=3, Thursday=4, Friday=5, Saturday=6)

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 the day will be the current weekday in day format.

PS: This would change according to when you’re reading this article.

I wrote this article on 01/04/2019, which is a Friday, so the result would be:

Friday

The default Keyword

The default keyword specifies the code to run if there is no case match, more like an else statement:

    switch (new Date().getDay()) {
      case 6:
        text = "Today is Saturday";
        break; 
      case 0:
        text = "Today is Sunday";
        break; 
      default: 
        text = "It's not the weekend yet!";
    }

The result of the text will be: It's not the weekend yet!.

The default case does not have to be the last case in a switch block:

    switch (new Date().getDay()) {
      default: 
        text = "Its not weekend yet!";
        break;
      case 6:
        text = "Today is Saturday";
        break; 
      case 0:
        text = "Today is Sunday";
    }

If the default is not the last case in the switch block, remember to end the default case with a break.

Conclusion

There are so many practical examples of switch cases. You can head here to learn more about switch cases.

Thanks for reading!

General ProgrammingJavaScriptES6