Clean Code Principles Every Developer Should Know

Table of Contents

• Why Clean Code Matters
• Meaningful Names
• Functions Should Do One Thing
• Comments: When to Write, When to Delete
• Don't Repeat Yourself (DRY)
• The Boy Scout Rule

Why Clean Code Matters

Code is read far more often than it is written. Studies suggest developers spend 10x more time reading code than writing it. Clean code isn't a luxury — it's the foundation of a sustainable codebase.

"Any fool can write code that a computer can understand. Good programmers write code that humans can understand." — Martin Fowler

Meaningful Names

Names should reveal intent. If a name requires a comment to explain it, rename it.

// Bad
const d = 86400; // seconds in a day
const u = getUser(1);

// Good
const SECONDS_IN_A_DAY = 86400;
const currentUser = getUserById(1);

Rules of thumb:

• Variables: nouns (userList, orderTotal)
• Functions: verbs (fetchUser, calculateTax)
• Booleans: questions (isActive, hasPermission)
• Avoid abbreviations like usr, cnt, tmp

Functions Should Do One Thing

The Single Responsibility Principle applied to functions: a function should do one thing, do it well, and do it only.

// Bad — does too much
async function processOrder(orderId) {
  const order = await db.orders.findById(orderId);
  order.total = order.items.reduce((sum, item) => sum + item.price, 0);
  await db.orders.update(orderId, order);
  await emailService.send(order.userEmail, 'Order confirmed');
  await analyticsService.track('order_processed', { orderId });
}

// Good — each function does one thing
async function processOrder(orderId) {
  const order = await fetchOrder(orderId);
  const updatedOrder = calculateOrderTotal(order);
  await saveOrder(updatedOrder);
  await notifyUser(updatedOrder);
  await trackOrderEvent(orderId);
}

Comments: When to Write, When to Delete

A comment that explains what code does is usually a sign that the code needs to be rewritten. A comment that explains why is often invaluable.

// Bad — the code already says this
// Loop through users
for (const user of users) { ... }

// Good — explains non-obvious reasoning
// Using a 400ms debounce to avoid hammering the search API
// while the user is still typing (measured optimal UX delay)
const debouncedSearch = debounce(search, 400);

Don't Repeat Yourself (DRY)

Every piece of knowledge should have a single, authoritative representation in the system. Duplication leads to bugs — fix it in one place, forget to fix it in three others.

// Bad — validation duplicated in two places
function createUser(email) {
  if (!email.includes('@')) throw new Error('Invalid email');
  // ...
}
function updateUser(email) {
  if (!email.includes('@')) throw new Error('Invalid email');
  // ...
}

// Good
function validateEmail(email) {
  if (!email.includes('@')) throw new Error('Invalid email');
}
function createUser(email) { validateEmail(email); /* ... */ }
function updateUser(email) { validateEmail(email); /* ... */ }

The Boy Scout Rule

"Always leave the code better than you found it."

You don't need a refactoring sprint. Every time you touch a file, make one small improvement: rename a confusing variable, extract a long function, delete a dead comment. Over time, these micro-improvements compound into a dramatically cleaner codebase.