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Safal Bhandari
Safal Bhandari

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Understanding Enums in TypeScript

Enums, short for enumerations, are a powerful feature in TypeScript that allow you to define a set of named constants. They provide a human-readable way to represent values that might otherwise be numbers or strings, making your code easier to read and maintain.

1. Why Use Enums?

Consider a game where you need to perform actions based on user input: pressing the up, down, left, or right arrow key. How would you represent these inputs in your code?

  • As strings: "UP", "DOWN", "LEFT", "RIGHT"
  • As numbers: 1, 2, 3, 4

Both work, but they are not very readable or self-explanatory. This is where enums shine.

2. Example: Using Enums for Directions

You can define an enum for directions like this:

enum Direction {
    Up,
    Down,
    Left,
    Right
}

function doSomething(keyPressed: Direction) {
    // perform an action based on the direction
}

doSomething(Direction.Up);
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✅ Advantages:

  • The code is cleaner and more readable.
  • You avoid "magic numbers" or ambiguous strings.

💡 At runtime, by default, enums store numeric values starting from 0. For example:

console.log(Direction.Up); // Output: 0
console.log(Direction.Right); // Output: 3
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3. Customizing Enum Values

You can change the numeric values if needed:

enum Direction {
    Up = 1,
    Down, // 2
    Left, // 3
    Right // 4
}
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Or you can use string enums for even clearer semantics:

enum Direction {
    Up = "UP",
    Down = "DOWN",
    Left = "LEFT",
    Right = "RIGHT"
}

doSomething(Direction.Down);
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4. Using Enums in Express Applications

Enums are also useful in web applications, such as defining HTTP response status codes:

enum ResponseStatus {
    Success = 200,
    NotFound = 404,
    Error = 500
}

app.get("/", (req, res) => {
    if (!req.query.userId) {
        res.status(ResponseStatus.Error).json({ error: "User ID missing" });
        return;
    }

    res.status(ResponseStatus.Success).json({ msg: "Request successful" });
});
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✅ Benefits:

  • Improves readability (ResponseStatus.Success is clearer than 200).
  • Reduces mistakes caused by hardcoding numbers or strings.

5. Summary

  • Enums provide named constants for better code clarity.
  • Default enums are numeric, starting from 0, but you can customize numbers or use strings.
  • Enums are widely used in TypeScript, including Express applications for status codes and other fixed sets of values.

Using enums is a simple but effective way to make your TypeScript code more maintainable and readable.

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