// What does this do?
const d = new Date();
const x = u.filter(i => i.a && !i.d);
 
// Obvious at a glance
const today = new Date();
const activeUsers = users.filter(user => user.isActive && !user.isDeleted);

// Does three things at once
async function processUser(userId: string) {
  const user = await db.user.findUnique({ where: { id: userId } });
  await sendWelcomeEmail(user.email);
  await db.user.update({ where: { id: userId }, data: { emailSent: true } });
  return user;
}
 
// Each function has one responsibility
async function getUser(userId: string) {
  return db.user.findUnique({ where: { id: userId } });
}
 
async function markEmailSent(userId: string) {
  return db.user.update({ where: { id: userId }, data: { emailSent: true } });
}
 
async function onboardUser(userId: string) {
  const user = await getUser(userId);
  await sendWelcomeEmail(user.email);
  await markEmailSent(userId);
  return user;
}

// What is 86400?
if (diff > 86400) expireSession();
 
// Self-documenting
const ONE_DAY_IN_SECONDS = 60 * 60 * 24;
if (diff > ONE_DAY_IN_SECONDS) expireSession();

// Useless
throw new Error("Invalid input");
 
// Actionable
throw new Error(`Invalid email format: "${email}". Expected format: user@domain.com`);

// Explains what (obvious from code)
// Loop through users
for (const user of users) { }
 
// Explains why (not obvious)
// Skip deleted users — soft deletes are preserved for audit compliance
for (const user of users.filter(u => !u.deletedAt)) { }