A practical guide to switch statements in JavaScript

It’s easy to feel overwhelmed by the different ways to approach decision-making in your JavaScript code, especially when working with conditional logic. Like everyone else, you might start with if...else statements.

But as your logic grows more complex, you’ll discover the switch statement in JavaScript is simply better for handling multiple conditions in a clean and readable way.

In this article, I’ll walk you through the ins and outs of switch statements: the basics of syntax, typical use cases like mapping values, a deep dive into the often-confusing fallthrough behavior, and how to manage it effectively with or without break statements.

What is a switch statement?

A switch statement is a control flow mechanism that enables your program to execute different blocks of code based on the value of a given expression. You can think of switch statements as a traffic controller; you provide a value, and the switch statement efficiently directs the execution flow to the appropriate code block, handling multiple potential conditions with ease.

This structure is particularly beneficial when you’re dealing with numerous specific cases, as it can make your code cleaner and more organized compared to a long chain of if...else statements.

Basic syntax of switch statements

At its core, the switch case in JS evaluates an expression once and then compares that result against a series of defined cases. Each case corresponds to a potential match, and the associated block of code is executed when a match is found. If none of the cases match, an optional default block can be used to handle any unexpected values or conditions.

Here’s the basic structure of a switch statement:

switch (expression) {
  case value1:
    // Code to execute if expression === value1
    break;
  case value2:
    // Code to execute if expression === value2
    break;
  default:
    // Code to execute if no cases match
}

The key elements of a switch statement are:

• expression – The value or condition you’re evaluating
• case – Each case checks if the expression matches a specific value
• break – Stops the execution of the switch block once a match is found. Without it, the code will “fall through” to the next case (more on this later)
• default – Optionally handles any situation where no case matches

Use cases for switch statements

Mapping values to actions

One common scenario for using a switch case in JS is when you need to map a set of input values to corresponding outputs or actions. For example, consider a function that handles user input or managing state in a game:

let direction = "left";

switch (direction) {
  case "up":
    console.log("Moving up");
    break;
  case "down":
    console.log("Moving down");
    break;
  case "left":
    console.log("Moving left");
    break;
  case "right":
    console.log("Moving right");
    break;
  default:
    console.log("Invalid direction");
}

By separating each possible direction into its case, the intent of the code is immediately obvious. It’s easy to add or remove cases without disrupting the overall structure.

Replacing multiple if...else statements

If you’ve ever written a bunch of if...else checks, you know how messy they can get. For example:

let day = "Monday";

if (day === "Monday") {
  console.log("Start of the workweek");
} else if (day === "Friday") {
  console.log("Almost the weekend!");
} else if (day === "Saturday" || day === "Sunday") {
  console.log("Weekend vibes!");
} else {
  console.log("Midweek days");
}

A switch can tidy this up nicely:

// Equivalent switch statement
switch (day) {
  case "Monday":
    console.log("Start of the workweek");
    break;
  case "Friday":
    console.log("Almost the weekend!");
    break;
  case "Saturday":
  case "Sunday":
    console.log("Weekend vibes!");
    break;
  default:
    console.log("Midweek days");
}

As you can see, the switch statement groups the different conditions under one variable, making the logic clearer and easier to read than several if...else blocks. It also handles multiple cases (like “Saturday” and “Sunday”) neatly by allowing them to share the same output without repeating code.

Fallthrough behavior in switch statements

One of the most notable quirks of a switch statement is fallthrough. If you don’t include a break (or another exit statement) in a switch statement, the code will continue to the next case — even if it doesn’t match.

While this can be a handy shortcut in some scenarios, it can also lead to unintended results if you forget to use break where it’s needed.

Let’s look at an example of fallthrough behavior being useful. In the following example, we want the same code to run for grades A, B, and C. By omitting break until after C, we conveniently group these cases:

let grade = "A";

switch (grade) {
  case "A":
  case "B":
  case "C":
    console.log("You passed!");
    break;
  case "D":
    console.log("You barely passed...");
    break;
  case "F":
    console.log("You failed.");
    break;
  default:
    console.log("Invalid grade");
}

Here, if grade is A, B, or C, the same block of code will execute. The same message — You passed! — is displayed. This is a clean way to group multiple cases.

On the flip side, here’s an example of unintentional fallthroughs causing unexpected behaviors:

let fruit = "apple";

switch (fruit) {
  case "apple":
    console.log("Apples are $0.50");
  case "orange":
    console.log("Oranges are $0.75");
    break;
  case "banana":
    console.log("Bananas are $0.25");
    break;
  default:
    console.log("Invalid fruit");
}

// Output:
// Apples are $0.50
// Oranges are $0.75

Since there’s no break after the apple case, the code “falls through” and executes the orange case as well, even though fruit is "apple". This might not be what you intended!

Switch vs. if...else: Which should you use?

The choice between a switch statement and an if...else chain often depends on the complexity of the conditions you’re evaluating. Here’s a table comparing them in detail:

Aspect	switch statement	if...else statement
Use case	Best when you are comparing the same expression against multiple specific values	Best when conditions are complex, involve ranges, or require evaluation of different expressions
Condition complexity	Ideal for simple equality checks	More flexible, accommodating complex conditions such as ranges or compound logic (e.g., if (x > 10 && x < 20)
Code readability	Offers a cleaner, more organized structure when dealing with many fixed-value cases, making the code easier to follow	Can become harder to read when multiple conditions are chained together, especially with nested or compound conditions
Evaluation	Evaluates a single expression once and compares it against defined cases	Evaluates each condition independently, which can be beneficial if different expressions need to be checked
Default behavior	Includes an optional default case to handle unmatched values, providing a clear fallback	Typically uses a final else block to catch any conditions that aren’t met by the preceding if and else if statements
Flexibility	Limited to checking the equality of a single expression	Highly flexible, allowing for a broader range of logical conditions and comparisons beyond mere equality

Advanced alternatives: Object literals

Although switch statements can be handy in many cases, there are other elegant JavaScript alternatives, like object literals. Object literals can simplify your code, reduce the risk of bugs caused by fallthrough, and make it easier to add or remove actions down the road. Here’s an example:

const actions = {
  play: () => console.log("Playing the music"),
  pause: () => console.log("Pausing the music"),
  stop: () => console.log("Stopping the music"),
  rewind: () => console.log("Rewinding the music"),
};

let command = "play";

actions[command] ? actions[command]() : console.log("Invalid command");

This approach is more concise and avoids the pitfalls of fallthrough. It’s also easier to extend; just add a new key-value pair to the object. If we consider the earlier example of mapping day numbers to day names, it can be rewritten with object literals as:

function getDayName(dayNumber) {
  const dayNames = {
    0: 'Sunday',
    1: 'Monday',
    2: 'Tuesday',
    3: 'Wednesday',
    4: 'Thursday',
    5: 'Friday',
    6: 'Saturday'
  };
  return dayNames[dayNumber] || 'Invalid day';
}

console.log(getDayName(3)); // Outputs: Wednesday

This method is not only shorter but also scales well when you simply need to map a set of keys to values. However, note that object literals are best used when dealing with direct mappings rather than when executing complex logic for each case.

Best practices for using switch statements

The following tactics will help you deploy switch statements to your advantage:

Always include a default case

A default case ensures that your code can handle unexpected or unrecognized values gracefully. This acts as a safety net; if none of the specified cases match, your program can still execute a fallback code block.

Use break to avoid fallthrough

Unless you intentionally want the execution to fall through to the next case, always include a break statement at the end of each case. This prevents unintentional behavior and makes your code logic clearer.

Keep it readable

If your switch statement grows too long or complex, consider refactoring your code into smaller, manageable functions or using an object literal. This improves readability and makes your code easier to maintain and debug.

Use descriptive case values

Choose meaningful and descriptive values in your case statements. This self-documenting approach makes it easier for anyone reading the code to understand the purpose behind each case, ultimately leading to better maintainability.

Common switch case pitfalls and how to avoid them

On the flip side, avoid these common switch case pitfalls:

Forgetting the break statement

As mentioned earlier, forgetting to include a break statement can lead to unintended fallthrough. Always double-check your switch statements to ensure each case ends with a break (unless a fallthrough is intentional).

Overusing switch statements

While switch statements are useful, they’re not always the best choice. If you find yourself writing a switch statement with dozens of cases, consider refactoring your code. Object literals or even a series of if...else statements might be more appropriate.

Ignoring the default case

The default case is your safety net. It ensures that your code handles unexpected values gracefully. Always include a default case, even if it’s just to log an error message.

Conclusion

The switch case in JS is a valuable addition to your JavaScript toolkit, offering a streamlined and organized way to handle multiple conditions. By using a switch statement, you can simplify your code structure, especially when mapping values to specific actions or replacing cumbersome if...else chains.

Remember, while switch statements can make your code cleaner, they require careful handling of fallthrough and consistent use of break and default cases to prevent unintended behavior.