JavaScript clean coding best practices - checklist

Why clean code matters for web development?

Writing clean code is essential for web development projects, especially as applications grow in complexity and scale. Clean code makes it easier for developers to understand and modify the codebase, improves collaboration, enhances performance, and reduces bugs and technical debt. By following clean code principles, developers can ensure that their code is maintainable, scalable, and efficient. Clean code practices are the foundation of a robust and reliable codebase, which makes it easier to onboard new team members and ensures that projects can evolve smoothly over time.

Below are 12 best and proven practices to make Javascriop code understandable and readable.

1. Consistent formatting

Use consistent indentation, spacing, and naming conventions throughout your code. Popular conventions include CamelCase for variables and functions and kebab-case for filenames.

// Variables and functions in CamelCase
const userAge = 25;
const maxUserLimit = 100;

function calculateTotalPrice(itemPrice, quantity) {
    return itemPrice * quantity;
}

// Helper function, used in getUserDetails
function findUserById(userId) {
    // Example implementation
    const users = [
        { id: 1, name: 'Alice', age: 30 },
        { id: 2, name: 'Bob', age: 25 }
    ];
    return users.find(user => user.id === userId);
}

// Using indentation and spacing
function getUserDetails(userId) {
    if (!userId) {
        return null;
    }

    const user = findUserById(userId);
    if (!user) {
        return null;
    }

    return {
        id: user.id,
        name: user.name,
        age: user.age
    };
}

// File names in kebab-case
// example files: user-profile.js, calculate-total-price.js

2. Descriptive names for variables and functions

Choose meaningful and descriptive names for variables, functions, and classes. This makes your code easier to understand.

Good variable name:

const maxUserLimit = 100;

Good function name:

function generateReportData(reportType, startDate, endDate) { /* ... */ }

Bad variable name:

const x = 100;

Bad function name:

function foo(a, b) { /* ... */ }

Choosing descriptive names is key to keeping code readable. Good names communicate the purpose of a piece of code, making it easier to maintain. Additionally, it is important to use modern JavaScript practices by advocating for the use of let and const instead of var. This approach enhances readability, ensures block scoping, and minimizes potential runtime errors, thereby improving code reliability.

3. Avoiding global scope pollution

Using global variables can cause conflicts and hard-to-debug issues. Always use let and const to define local variables within their scope. When necessary, use Immediately Invoked Function Expressions (IIFE) to create isolated scopes.

Example:

(function() {
    const localVar = "This is local and safe";
})();
// localVar is not accessible here

4. Add comments to explain blocks of code

Comments play a key role in writing good code. They make it easier to understand what a piece of code does and why it was written a certain way.

Be sure to comment on all relevant parts of the code, not just those that may be difficult to understand. Well-placed comments can significantly speed up the debugging process and make future modifications easier. However, strive for self-documenting code first—your code should be clear enough that extensive comments are not needed. Use comments to explain the why rather than the what.

Example:

/**
* Fetches user details from the database.
* @param {number} userId - The ID of the user.
*/
function fetchUserDetails(userId) {
    // Fetching user details from API
    // The userId must be greater than 0
    if (userId <= 0) throw new Error("Invalid user ID");
    // ... implementation
}

5. Write modular code that can be reused

Divide your code into smaller, reusable modules or functions. This promotes code reuse and helps manage complexity. Modularizing your code also prevents duplication—if you create a universal function, you can easily apply it to different parts of the project.

Example:

function calculateArea(width, height) {
    return width * height;
}

function calculateVolume(width, height, depth) {
    return calculateArea(width, height) * depth;
}

Modular code allows for single-responsibility functions, making your code more maintainable.

6. Best practices for asynchronous code

Use async/await to handle asynchronous operations instead of deeply nested callbacks (i.e., callback hell) or complex Promise chains. Always use try...catch blocks to manage errors in async functions.

Example:

async function fetchData() {
try {
const response = await fetch('https://api.example.com/data');
const data = await response.json();
console.log(data);
} catch (error) {
console.error('Failed to fetch data:', error);
}
}

Using async/await makes asynchronous code look and behave more like synchronous code, improving readability.

7. Avoiding code smells and anti-patterns

Code smells are symptoms of deeper problems in your codebase. Examples of code smells include:

• Magic Numbers: Use named constants instead of hard-coded numbers.
• Overuse of Global Variables: Limit globals as they can lead to bugs and make maintenance harder.

Example:

// Bad practice
if (user.age > 21) {
    // do something
}

// Good practice
const LEGAL_AGE = 21;
if (user.age > LEGAL_AGE) {
    // do something
}

Named constants make the purpose of numbers clear and improve readability.

8. Comprehensive error handling

Proper error handling is crucial for building reliable software. Use try...catch blocks to manage errors and, where necessary, create custom error classes for better error differentiation.

Example:

class CustomError extends Error {
    constructor(message, statusCode) {
        super(message);
        this.statusCode = statusCode;
    }
}

try {
    throw new CustomError("Resource not found", 404);
} catch (error) {
    if (error instanceof CustomError) {
        console.error(`Custom error occurred: ${error.message}, Status: ${error.statusCode}`);
    }
}

Custom error classes help differentiate between various error types, which allows for more nuanced error handling.

9. Testing javaScript code

Testing is an essential part of writing reliable code. Use testing frameworks like Jest or Mocha to create unit tests, ensuring that your functions behave as expected.

Example:

// Using Jest for unit testing
function sum(a, b) {
    return a + b;
}

module.exports = sum;
const sum = require('./sum');

test('adds 1 + 2 to equal 3', () => {
    expect(sum(1, 2)).toBe(3);
});

Testing ensures your code is stable and makes it easier to refactor without introducing bugs.

10. Avoid irrelevant classes and understand hoisting

Avoid creating unnecessary classes. Only use classes when the object-oriented model is necessary. Additionally, understand that classes are not hoisted like functions.

Example:

// Bad practice
const hat = new Product("red hat", 1000); // ReferenceError
class Product {
    constructor(name, price) {
        this.name = name;
        this.price = price;
    }
}

// Correct order
class Product {
    constructor(name, price) {
        this.name = name;
        this.price = price;
    }
}
const hat = new Product("red hat", 1000);

Always declare classes before you use them.

11. Use libraries and frameworks

Using libraries and frameworks is crucial for writing clean and readable JavaScript code. Tools like Lodash and frameworks like React or Vue.js can help enforce standards, promote modularization, and avoid reinventing the wheel.

Example with Lodash:

const _ = require('lodash');

const users = [
    { user: 'Alice', age: 25 },
    { user: 'Bob', age: 30 }
];

const sortedUsers = _.sortBy(users, ['age']);
console.log(sortedUsers);

Libraries save time and help avoid errors by leveraging community-tested solutions.

12. Refactoring techniques

Refactoring keeps your code clean over time. Techniques like extracting functions, renaming variables, and removing duplication help maintain the quality of the codebase.

Example:

// Original code
function processUserData(user) {
    // Get full name
    const fullName = `${user.firstName} ${user.lastName}`;
    // Log welcome message
    console.log(`Welcome, ${fullName}!`);
}

// Refactored code
function getFullName(user) {
    return `${user.firstName} ${user.lastName}`;
}

function logWelcomeMessage(user) {
    console.log(`Welcome, ${getFullName(user)}!`);
}

Refactoring code makes it more modular, easier to test, and more maintainable over time.

FAQ – Frequently Asked Questions

What tools can I use to ensure the cleanliness and consistency of my JavaScript code?
Use tools like ESLint for linting and Prettier for code formatting. They help ensure consistency and prevent common mistakes.

How can I improve the performance of my JavaScript code while maintaining readability?
Use debouncing, throttling, and optimize loops. Minimize direct DOM manipulations and use requestAnimationFrame for smoother animations.

What are the best practices for code organization in large JavaScript projects?
Follow modularization practices, use helper functions, and adopt the stepdown rule to structure code in a natural, readable order.

How do I ensure that my JavaScript code is well tested?
Use testing frameworks like Jest, Mocha, or Cypress. Follow TDD (Test-Driven Development) to ensure your code is thoroughly tested before integrating new features.