Como escrever código limpo: 12 princípios que todo desenvolvedor deve saber em 2026

Error 504 (Server Error)!!1504.That’s an error.There was an error. Please try again later.That’s all we know.

Error 504 (Server Error)!!1504.That’s an error.There was an error. Please try again later.That’s all we know.

// ❌ Unclear
const d = new Date();
const arr = users.filter(u => u.a);
function proc(x) { return x * 86400; }

// ✅ Clear
const currentDate = new Date();
const activeUsers = users.filter(user => user.isActive);
function convertDaysToSeconds(days) { return days * 86400; }

Error 504 (Server Error)!!1504.That’s an error.There was an error. Please try again later.That’s all we know.

Error 504 (Server Error)!!1504.That’s an error.There was an error. Please try again later.That’s all we know.

// ❌ Function does too much
async function processUserRegistration(data) {
  // validates, saves to DB, sends email, creates audit log
  if (!data.email.includes('@')) throw new Error('Invalid email');
  const user = await db.users.create(data);
  await sendWelcomeEmail(user.email);
  await auditLog.record('USER_CREATED', user.id);
  return user;
}

// ✅ Each function has one responsibility
async function createUser(data) {
  validateUserData(data);
  return db.users.create(data);
}

async function onUserCreated(user) {
  await Promise.all([
    sendWelcomeEmail(user.email),
    auditLog.record('USER_CREATED', user.id)
  ]);
}

// Orchestrator is easy to read
async function registerUser(data) {
  const user = await createUser(data);
  await onUserCreated(user);
  return user;
}

Error 504 (Server Error)!!1504.That’s an error.There was an error. Please try again later.That’s all we know.

// ❌ Too many positional args — easy to mix up order
function createEvent(title, date, location, maxAttendees, isPublic, category) {}
createEvent("Meeting", "2026-07-01", "NYC", 50, true, "work");

// ✅ Use an options object for 3+ params
function createEvent({ title, date, location, maxAttendees = 100, isPublic = true, category }) {}
createEvent({ title: "Meeting", date: "2026-07-01", location: "NYC", category: "work" });

Error 504 (Server Error)!!1504.That’s an error.There was an error. Please try again later.That’s all we know.

// ❌ Mutating data in place
function addDiscount(order, discountRate) {
  order.total = order.total * (1 - discountRate);  // mutates original
  order.hasDiscount = true;
  return order;
}

// ✅ Return a new object
function addDiscount(order, discountRate) {
  return {
    ...order,
    total:       order.total * (1 - discountRate),
    hasDiscount: true
  };
}

Error 504 (Server Error)!!1504.That’s an error.There was an error. Please try again later.That’s all we know.

// ❌ Deep nesting
function processPayment(user, amount, card) {
  if (user) {
    if (user.isActive) {
      if (amount > 0) {
        if (card.isValid) {
          return charge(card, amount);
        } else { return { error: 'Invalid card' }; }
      } else { return { error: 'Invalid amount' }; }
    } else { return { error: 'Inactive user' }; }
  } else { return { error: 'No user' }; }
}

// ✅ Early returns eliminate nesting
function processPayment(user, amount, card) {
  if (!user)            return { error: 'No user' };
  if (!user.isActive)   return { error: 'Inactive user' };
  if (amount <= 0)      return { error: 'Invalid amount' };
  if (!card.isValid)    return { error: 'Invalid card' };
  return charge(card, amount);
}

Error 504 (Server Error)!!1504.That’s an error.There was an error. Please try again later.That’s all we know.

// ❌ Copy-pasted validation in 5 places
function createUser(data) {
  if (!data.email || !data.email.includes('@')) throw new Error('Invalid email');
  if (!data.name || data.name.length < 2) throw new Error('Name too short');
  // ...
}
function updateUser(data) {
  if (!data.email || !data.email.includes('@')) throw new Error('Invalid email');
  if (!data.name || data.name.length < 2) throw new Error('Name too short');
  // ...
}

// ✅ Single validation function
function validateUserData({ email, name }) {
  if (!email?.includes('@'))   throw new Error('Invalid email');
  if (!name || name.length < 2) throw new Error('Name too short');
}
function createUser(data) { validateUserData(data); /* ... */ }
function updateUser(data) { validateUserData(data); /* ... */ }

Error 504 (Server Error)!!1504.That’s an error.There was an error. Please try again later.That’s all we know.Error 504 (Server Error)!!1504.That’s an error.There was an error. Please try again later.That’s all we know.

Error 504 (Server Error)!!1504.That’s an error.There was an error. Please try again later.That’s all we know.

// ❌ Explains what (code already does this)
// Multiply price by tax rate and add to price
const total = price + (price * taxRate);

// ❌ Outdated comment (code changed, comment didn't)
// Returns user's first name
function getUserDisplayName(user) {
  return user.displayName ?? user.email;  // changed to prefer displayName
}

// ✅ Explains non-obvious why
// Delay ensures animation frame is painted before measuring
// Without this, getBoundingClientRect returns 0
requestAnimationFrame(() => {
  const height = element.getBoundingClientRect().height;
});

Error 504 (Server Error)!!1504.That’s an error.There was an error. Please try again later.That’s all we know.

// ❌ Silent failure — caller doesn't know something went wrong
async function getUser(id) {
  try {
    return await db.users.findById(id);
  } catch (err) {
    return null;  // caller can't distinguish "not found" from "DB error"
  }
}

// ✅ Explicit error types
class UserNotFoundError extends Error {
  constructor(id) {
    super(`User ${id} not found`);
    this.name = 'UserNotFoundError';
    this.code = 'USER_NOT_FOUND';
  }
}

async function getUser(id) {
  const user = await db.users.findById(id);
  if (!user) throw new UserNotFoundError(id);
  return user;
}

Error 504 (Server Error)!!1504.That’s an error.There was an error. Please try again later.That’s all we know.

Error 504 (Server Error)!!1504.That’s an error.There was an error. Please try again later.That’s all we know.

Error 504 (Server Error)!!1504.That’s an error.There was an error. Please try again later.That’s all we know.

// ❌ Magic boolean parameters
renderButton(true, false, true);  // what do these mean?
user.update({ 1: true });

// ✅ Named boolean parameters or enums
renderButton({ isPrimary: true, isDisabled: false, showIcon: true });
user.setActiveStatus(UserStatus.ACTIVE);

Error 504 (Server Error)!!1504.That’s an error.There was an error. Please try again later.That’s all we know.

// ❌ Mixes high-level and low-level in same function
async function checkout(cart) {
  const total = cart.items.reduce((sum, item) => sum + item.price * item.qty, 0);
  const taxRate = 0.08;
  const tax = total * taxRate;
  await db.query('INSERT INTO orders (total, tax) VALUES ($1, $2)', [total, tax]);
  await emailService.send({ to: cart.user.email, subject: 'Order confirmed' });
}

// ✅ Each function at one abstraction level
async function checkout(cart) {
  const order = calculateOrderTotals(cart);
  await persistOrder(order);
  await notifyCustomer(cart.user, order);
}

Error 504 (Server Error)!!1504.That’s an error.There was an error. Please try again later.That’s all we know.

Error 504 (Server Error)!!1504.That’s an error.There was an error. Please try again later.That’s all we know.

Error 504 (Server Error)!!1504.That’s an error.There was an error. Please try again later.That’s all we know.

Error 504 (Server Error)!!1504.That’s an error.There was an error. Please try again later.That’s all we know.
Error 504 (Server Error)!!1504.That’s an error.There was an error. Please try again later.That’s all we know.

Error 504 (Server Error)!!1504.That’s an error.There was an error. Please try again later.That’s all we know.
Error 504 (Server Error)!!1504.That’s an error.There was an error. Please try again later.That’s all we know.

Error 504 (Server Error)!!1504.That’s an error.There was an error. Please try again later.That’s all we know.
Error 504 (Server Error)!!1504.That’s an error.There was an error. Please try again later.That’s all we know.

Error 504 (Server Error)!!1504.That’s an error.There was an error. Please try again later.That’s all we know.
Error 504 (Server Error)!!1504.That’s an error.There was an error. Please try again later.That’s all we know.

Error 504 (Server Error)!!1504.That’s an error.There was an error. Please try again later.That’s all we know.
Error 504 (Server Error)!!1504.That’s an error.There was an error. Please try again later.That’s all we know.

Error 504 (Server Error)!!1504.That’s an error.There was an error. Please try again later.That’s all we know.

Error 504 (Server Error)!!1504.That’s an error.There was an error. Please try again later.That’s all we know.