The Switch Statement

The Switch statement is a convenient way of handling situations where you need to handle many actions based on the value of a variable. The Switch statement starts of with the switch statement which contains an expression that should evaluate into a number. After the switch statement is a block of code which consists of case statements and an optional default statement.

switch (number)

{

     case 1:

           console.log("The number is one");

           break;

     case 2:

           console.log("The number is two");

           break;

     case 3:

           console.log("The number is three");

           break;

     default:

           console.log("The number is not one, two or three");

}

After each of the case statements is the code you want to execute if the variable being switched equals the value of the case. The code should end with a break statement, which causes the program to skip over the rest of the switch block. If there is no break statement, all code in the following case statement will also be executed. In some cases, this is exactly what you want to happen, as it allows you to define a group of numbers that all do the same action. Forgetting the break statement is a very common mistake for beginners to make and is even something that experts have made resulting in devastating results.

The default statement will be executed if none of the case statements match the value of the switch expression. No break statement is needed after the default code, though I usually do have a break statement out of habit. While the default statement is optional, it is a good habit to always have a default action, even if the default is simply a trace statement telling you that you have reached code that should not be reached.

The switch statement we have above could be done with if statements as you can see below.

if (number == 1) {

    console.log("The number is one");

} else if (number == 2) {

    console.log("The number is two");

} else if (number == 3) {

    console.log("The number is three");

} else {   

     console.log("The number is not one, two or three");

}

The choice between using switch and if statements is more of a cosmetic one with JavaScript. Switch statements are a convenience statement designed to replace large numbers of if then else statements in a more readable way.

The switch statement comes directly from the C programming language. While I am a fan of that language, being one of the first programming languages that I learned, I have been bitten by the switch statement too many times and have uncovered bugs in other people’s code due to the forgetting of a break statement frequently. Therefore, I am happy that new languages are replacing the default fall-through behavior with default break behavior requiring a statement to fall through.

Another common bug with the switch statement is not having a default block when a case does not cover all possibilities. The result of not having a default is essentially a default that does nothing which may be what you want. It could also be an indication that you expect only the values in the case to exist. Having a default that reports an error if it is reached is recommended in this situation.