In this lesson, you'll explore the benefits of writing small functions in JavaScript and how they contribute to clean, maintainable code. Small functions are a cornerstone of good software design, promoting readability, reusability, and ease of testing. Let's dive into why small functions matter and how to effectively implement them in your code.

Small Functions

Do One Thing (DOT) Principle

The Do One Thing principle, often referred to as Curly’s Law, suggests that functions should perform a single task. This approach ensures that each function is focused and easy to understand. A function should either perform an action or return a result, but not both.

Example: A function named should only handle updating user information, not fetching or saving it.

Consistency in Abstraction Levels

According to the Same Level of Abstraction Principle (SLAP), all code within a function should operate at the same level of abstraction. This consistency makes the code easier to read and understand. Mixing different levels of abstraction within a single function can lead to confusion.

Guidelines for Writing Small Functions

Keep It Short and Sweet

• Screen Fit: Aim for functions that fit on a single screen with a reasonable font size. This makes them easier to read and understand.
• Three Blocks Rule: Limit functions to about three logical blocks or "paragraphs" of code. Each block should represent a distinct step in the function's process.

Avoid Repetition

• DRY Principle: Longer functions often contain repetitive code. By keeping functions small, you can eliminate redundancy and make the code more efficient.

Facilitate Testing and Debugging

• Unit Testing: Smaller functions are easier to test individually, allowing for more precise debugging and validation of functionality.
• Refactoring: Small functions simplify the process of refactoring, making it easier to improve code quality over time.

Enhance Readability

• Readable Code: Code that reads like a story is easier to maintain and extend. Small functions contribute to this by breaking down complex logic into manageable pieces.

Addressing Concerns About Small Functions

Some argue that shorter functions may lead to higher defect density or make debugging harder. However, with modern practices like Test-Driven Development (TDD) and powerful development tools, these concerns are mitigated. Readable code is inherently easier to maintain, and small functions support this goal.

When to Refactor

If writing small functions disrupts your workflow, start with a longer function and refactor it into smaller parts. Use your IDE's refactoring tools to extract methods and move them between classes until the code is clear and concise.

Conclusion

There is no strict rule for how many lines a function should have, but the goal is to keep functions as short as possible while maintaining clarity. Small functions enhance readability, facilitate testing, and reduce complexity, making your codebase more robust and maintainable. Remember, the effort you put into writing small, focused functions today will pay off in the long run, making your projects more successful and enjoyable to work on.