Functions should do one thing

Usage

📝 Guideline

Functions should do one thing: Create a function for each action or concept. Functions should do one and only one thing.

A function in clean code should have a clear purpose and perform a single task. It should not be responsible for multiple actions or concepts. By following this principle, your code becomes more modular, readable, and maintainable.

🛠️ How to apply

• Each function should have a clear and specific purpose, focusing on a single task. 🎯
• Avoid including multiple functionalities or responsibilities within a single function. 🚫
• Aim to keep your functions concise and easily understandable. 📚
• Refactor complex functions into smaller, modular ones, each handling a specific task. 🔧
• Avoid functions that need "and," "or," or "if" to indicate multiple tasks or conditions. ⛔

Pros and Cons

👍 Pros

• Improved code organization: By adhering to this principle, your codebase becomes more structured and easier to navigate. 📂
• Enhanced reusability: Well-defined functions that perform a single task can be easily reused in different parts of your application. 🔄

👎 Cons

• Increased function count: Applying this principle may lead to a larger number of functions within your codebase, which could make it more challenging to manage for larger projects. ⚙️
• Potential performance impact: Dividing complex tasks into smaller functions may introduce additional function calls and, in some cases, slightly affect performance. 🐢

Examples

❌ Bad

// Bad: Function performing multiple tasks
function processAnimal(animal: string): void {
    if (animal === 'cat') {
        console.log('Meow!');
        feedCat();
    } else if (animal === 'dog') {
        console.log('Woof!');
        walkDog();
    } else {
        console.log('Unknown animal!');
    }
}

// Bad: Function performing multiple tasks
function processAnimal(animal: string): void {
    if (animal === 'cat') {
        console.log('Meow!');
        feedCat();
    } else if (animal === 'dog') {
        console.log('Woof!');
        walkDog();
    } else {
        console.log('Unknown animal!');
    }
}

✅ Good

// Good: Functions performing a single task
function makeSound(animal: string): void {
    if (animal === 'cat') {
        console.log('Meow!');
    } else if (animal === 'dog') {
        console.log('Woof!');
    } else {
        console.log('Unknown animal!');
    }
}
 
function feedCat(): void {
    console.log('Feeding the cat...');
}
 
function walkDog(): void {
    console.log('Walking the dog...');
}

// Good: Functions performing a single task
function makeSound(animal: string): void {
    if (animal === 'cat') {
        console.log('Meow!');
    } else if (animal === 'dog') {
        console.log('Woof!');
    } else {
        console.log('Unknown animal!');
    }
}
 
function feedCat(): void {
    console.log('Feeding the cat...');
}
 
function walkDog(): void {
    console.log('Walking the dog...');
}

Related principles

• Separation of concerns: Functions should focus on specific tasks, promoting a modular and organized codebase. 🧩
• Single Responsibility Principle: Each function should have a single responsibility, contributing to maintainable and reusable code. 🎛️
• KISS (Keep It Simple, Stupid): Strive for simplicity in design and implementation. 🤏