javascript-coding-standards

JavaScript Coding Standards

Quick Navigation: Level 1: Quick Start (5 min) → Level 2: Implementation (30 min) → Level 3: Mastery (Extended)

Level 1: Quick Start (<2,000 tokens, 5 minutes)

Core Principles

1. Modern JavaScript: Use ES6+ features (arrow functions, destructuring, async/await)
2. Type Safety: Use TypeScript or JSDoc for type annotations where complexity warrants
3. Test-First: Write Jest tests before implementation
4. Clean Code: Follow Airbnb style guide, use meaningful names
5. Modern Tooling: ESLint + Prettier for consistent formatting

Essential Checklist

• ESLint + Prettier: Code formatted and linted automatically
• Modern Syntax: Arrow functions, const/let (no var), template literals
• Testing: Jest tests with >80% coverage
• Documentation: JSDoc for complex functions and public APIs
• Error Handling: Try/catch for async operations, proper error types
• Security: Input validation, no eval(), sanitize user input
• Module System: ES6 modules (import/export), not CommonJS
• Dependencies: package.json with exact versions, npm audit passing

Quick Example

/**
 * User authentication module with secure session handling.
 * @module auth
 */

import bcrypt from 'bcrypt';
import jwt from 'jsonwebtoken';

/**
 * Authenticate user with username and password.
 *
 * @param {string} username - User's username
 * @param {string} password - Plain text password
 * @returns {Promise<{success: boolean, token?: string, error?: string}>}
 * @throws {ValidationError} If credentials are invalid
 *
 * @example
 * const result = await authenticateUser('alice', 'secret123');
 * if (result.success) {
 *   console.log('Token:', result.token);
 * }
 */
export const authenticateUser = async (username, password) => {
  // Validate inputs
  if (!username || !password) {
    throw new ValidationError('Username and password required');
  }

  try {
    // Fetch user from database
    const user = await fetchUserFromDb(username);

    if (!user) {
      return { success: false, error: 'Invalid credentials' };
    }

    // Verify password
    const isValid = await bcrypt.compare(password, user.passwordHash);

    if (!isValid) {
      return { success: false, error: 'Invalid credentials' };
    }

    // Generate JWT token
    const token = jwt.sign(
      { userId: user.id, username: user.username },
      process.env.JWT_SECRET,
      { expiresIn: '1h' }
    );

    return { success: true, token };
  } catch (error) {
    console.error('Authentication error:', error);
    throw new AuthenticationError('Authentication failed', error);
  }
};

/**
 * Custom validation error.
 */
class ValidationError extends Error {
  constructor(message) {
    super(message);
    this.name = 'ValidationError';
  }
}

/**
 * Custom authentication error.
 */
class AuthenticationError extends Error {
  constructor(message, cause) {
    super(message);
    this.name = 'AuthenticationError';
    this.cause = cause;
  }
}