Mastering the JavaScript switch Statement — SitePoint

The JavaScript switch statement is a way to make decisions in your code based on different conditions. It is a more organized and concise alternative to using multiple if-else statements. The switch statement evaluates a given expression, which can be a variable or a value, and compares it to several possible cases. If the value of the expression matches one of the cases, the associated code block (a set of instructions) is executed. If no match is found, an optional default case can be executed as a fallback, meaning it runs when none of the other cases apply.

For example, here’s a simple switch statement that checks the value of a variable called day:

By mastering switch statements, you can write cleaner, more efficient, and better-organized JavaScript code, ultimately improving your overall programming skills.

switch statements begins with the keyword switch, followed by an expression in parentheses. This expression is compared to a series of case labels enclosed in a switch block. Each case label represents a distinct value, and the code block that follows the case is executed when the expression matches the case label’s value. A break statement is typically used to exit the switch block after a matching case is executed, ensuring that only the intended code block runs, and preventing fall-through to the next cases. Optionally, a default case can be included to provide a fallback action when none of the case labels match the expression, ensuring a response for unknown values.

The switch statement is an alternative to using if-else statements when you have multiple conditions to handle. While if-else statements are suitable for checking a series of conditions that can be expressed as true or false, switch statements are more efficient when dealing with a single expression that can take on multiple distinct values. In essence, switch statements can make your code cleaner, more organized, and easier to read when you have several related conditions to manage.

For example, consider the following if-else structure:

The equivalent switch statement would look like this:

The switch statement offers a more organized and readable way to handle multiple conditions, particularly when dealing with a large number of cases. In a switch statement, the expression being evaluated is the variable or value inside the parentheses (in this example, the variable color).

Both switch and if-else solve similar problems and have advantages and disadvantages based on your use cases. To help you make your decision, I’ve created a simple switch statement:

The switch statement provides additional functionality and concepts that can be used to improve the performance, readability, and conciseness of your code.

The default case in a switch statement is executed when none of the other cases match the provided expression. It serves as a fallback to handle unexpected or unknown values, ensuring a response is provided even if there’s no matching case.

The break keyword is used in a switch statement to exit the switch block once a matching case is found and executed. It prevents the code from continuing to execute the remaining cases, ensuring only the correct output is generated.

A case cannot have more than one condition in a switch statement. To incorporate multiple conditions in one case, consider using the fall-through technique. Not only does it save you time, it ensure you don’t repeat yourself.

Fall-through in a switch statement occurs when you intentionally omit the break keyword in a case, allowing the code execution to continue to the next case(s) until a break is encountered or the end of the switch block is reached. This can be useful when multiple cases share the same output or action.

A frequent mistake when using switch statements is not including the break statement after each case. This error results in unintentional fall-through, executing multiple cases instead of just the desired one.

How to fix it: Add a break statement after each case to prevent fall-through.

Switch statements use strict comparison, which can lead to unexpected results when comparing different data types. In the example below, the string "2" is not equal to the number 2. This pitfall might cause your cases not to execute as intended.

How to fix: Consider the type of your variables and remember it will be evaluated strictly. TypeScript may help if you’re working on larger projects.

A common pitfall in switch statements is declaring variables without block scope or incorrect scopes, causing them to be accessible in other cases, or creating syntax errors. You may experience an Uncaught SyntaxError: ... if you try to redeclare the same variable in multiple clauses.

The fixes:

Block scope your clauses:

Now that you know what a switch statement is, how it works, and when to use it, it’s time to start implementing it! I hope you’ve enjoyed this article. Join us over on the SitePoint Community if you have any questions about this piece or JavaScript in general.

Mark is the General Manager of SitePoint.com. He loves to read and write about technology, startups, programming languages, and no code tools.