SOLID Principles

What You'll Cover Today

Day 3 of Clean Code in 5 Days focuses on solid principles. Each SOLID principle explained with before/after code examples. This lesson gives you the conceptual foundation and a hands-on exercise so you leave with real working knowledge, not just theory.

SOLID

Understanding solid is foundational for everything in this course. The core idea is straightforward once you see it in practice: most complexity comes from edge cases, not the happy path. Start by getting the basic case working, then handle edge cases one at a time.

// SOLID Principles — working example
// Replace these values with your actual data

const example = {
  topic: 'SOLID',
  day: 3,
  course: 'Clean Code in 5 Days'
};

// This is where your implementation goes
function implement(config) {
  // 1. Validate inputs
  if (!config.topic) throw new Error('Topic required');
  
  // 2. Core logic
  const result = process(config);
  
  // 3. Return structured output
  return result;
}

console.log('Ready to implement SOLID');

OCP

Once you have the basics, ocp becomes the practical application. The pattern you'll use most often is: configure once, reuse everywhere. Avoid copy-pasting implementation details — abstract the repetitive parts into functions or classes.

Common Mistakes on Day 3

• Skipping error handling — every real-world implementation needs error handling. Add it from the start, not as an afterthought.
• Hard-coding configuration — use environment variables for anything that differs between development and production.
• Not reading error messages — error messages in Clean are usually precise. Read them carefully before searching Stack Overflow.
• Over-abstracting too early — make it work first, then refactor. Premature abstraction is the enemy of progress.