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JavaScript - How to Use switch Statements in JavaScript

A switch statement is a form of a conditional statement. It will execute a code block if a certain condition is met.

Switch statements are used when you want different actions or results to occur for different situations. They are similar to using if…else statements to handle multiple alternative outcomes in the code.

The switch statement matches an expression’s value to cases by order. It will either execute the code for a matching case, or an optional default code if no matches are found.

Basic switch example

Below is a basic switch statement example:

const numOfItems = 2;
switch (numOfItems) {
    case 3:
        console.log('Get one free item!!');
        break;
    case 2:
    case 1:
        console.log('The fourth item is free!!');
        break;
    default:
        console.log('Today only, 3 + 1 free!!');
}
// Expected output: The fourth item is free!!

In the example above, const numOfItems represents the number of items in a user’s cart, two items in this case.

The switch statement uses the strict equality operator (===) to evaluate each condition in turn. Conditions are defined using the case keyword. The switch statement begins with the top condition, checking numOfItems against the value 3. Since these two values are not equal, the statement switches to the next case, where the value is equal (2). This results in the following code being executed until a break statement is encountered. In the example above while case 2 has no associated code defined, the code in case 1 is executed as it occurs after the matching case has been encountered. This results in “The fourth item is free!!” being printed to the console. The break statement that follows stops the procedure; if omitted, the program will continue to execute the following statements until it encounters either the next break statement or the end of the switch statement. In the example above, if the second break was omitted the text “Today only, 3 + 1 free!!” would have also been printed to the console.

It is possible to use the same result code for multiple cases, as seen in the example above – both cases 2 and 1 print the text ‘The fourth item is free!!’ to the console.

Any other value, (e.g. 0, ‘x’, and even 4) will result in the default case executing. In these cases, the final console.log() statement will execute, printing “Today only, 3 + 1 free!!” to the console.

Note: Passing this code a value of 4 creates a problem in how the cases are evaluated. This issue is explored below in the section Using switch with conditions other than strict equality.

Before we explore this problem, let’s take a look at the syntax for switch statements.

Syntax

The switch statement receives an expression, which is evaluated once. It then checks for matching values in the different cases provided. When a match is found, the statements associated with that case are executed. If no match is found, nothing will happen unless a default clause is provided. When a default clause is included, the statements associated with the default clause are executed when no match is found.

switch (expression) {

case value1:

statement(s) to execute

break;

case value2:

statement(s) to execute

break;

case valueN:

statement(s) to execute

break;

default:

statement(s) to execute

}

expression: an expression, which will be evaluated once at the beginning of the process. The value of this expression is compared against the following cases.

case values (1 thru N): each case needs to have a specified value and a set of executable statements. The values are strictly compared (===) to the expression, and when there is a match the associated statements for the case are executed.

break (optional): the break statement stops the execution process and exits the switch statement.

Once a case value comparison returns true, all of the following statements are set for execution. The break statement prevents all of the statements from being executed, stopping execution when the break statement is encountered. By placing this statement at the end of each set of statements for a case, you can ensure only the statement(s) associated with the specific matched case are executed.

default (optional): this statement will be executed if all other comparisons returned false. This clause is usually found at the bottom of a switch statement, but it is not mandatory.

Note: If the default clause is not the last clause in the switch statement, make sure to add a break statement at the end of the statements intended to be executed for the default case.

Using switch with conditions other than strict equality

If you wish, you can use comparison operators other than strict equality. The comparison expression used must evaluate to a Boolean value (therefore logical operators can be applied as well).

For example, let’s say that in the example above we want to print the text “Get one free item!!” to the console whenever the number of items is equal to or greater than 3. A first iteration of this approach might look like the following: case >= 3:

Unfortunately, this code will result in an error – Uncaught SyntaxError: Unexpected token ‘>=’ .

Parentheses will not help in this situation, as the issue lies in defining the left-hand-side of the >= operand. To resolve this, we need to instead provide a complete comparison expression that can evaluate to a Boolean value.

The following example demonstrates how to achieve this type of relative comparison:

const numOfItems = 2;
switch (true) {
    case (numOfItems >= 3):
        console.log('Get one free item!!');
        break;
    case (numOfItems >= 1):
        console.log('The fourth item is free!!');
        break;
    default:
        console.log('Today only 3 + 1!!');
}
// Expected output: The fourth item is free!!

In the code above, whenever the case’s expression evaluates to true, there is a match and the case’s statement(s) will be executed. In the case of numOfItems = 4, both of the first two cases return true. However, due to the break statement at the end of the first case, the second case will not be read and its statement will not be executed.

switch vs if…else

switch statements and if…else statements are in many ways functionally equivalent. Both types of statements can produce similar results, and in many cases programmers simply choose to use the version they are more comfortable with. switch statements are arguably clearer and more readable when there are many conditions to choose from, but the choice of statement is still largely a matter of personal preference.

The above switch statement rewritten, as an if…else statement, would match the example below:

if (numOfItems >= 3) console.log('Get one free item!!');
else if (numOfItems >= 1) console.log('The fourth item is free!!');
else console.log('Today only 3 + 1!!');

switch with no break statements example

Let’s say you are writing a code that issues prizes for a contest in a game. In this game, the first place winner gets all of the prizes, while each successive lower ranking results in one less prize being granted. Code to implement this could resemble the following:

const rank = 1;
switch (rank) {
    case 1:
        console.log('Invisibility ring, ');
    case 2:
        console.log('Healing potion, ');
    case 3:
        console.log('Treasure chest, ');
    default:
        console.log('5 Gold bars');
}
// Expected output:
// Invisibility ring, 
// Treasure chest, 
// Healing potion, 
// 5 Gold bars

Note that the example above uses no break statements. As there are no break statements present, when a clause’s case value matches the expression, all of the following statements are executed. According to the code above, a user who came in 4th or after will only receive the 5 gold bars (due to the default clause), while by comparison a user in 2nd place will receive the healing potion, the treasure chest, and the 5 gold bars.

 

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