code-quality

Code Quality

This skill provides code quality principles and best practices for reviewing and improving implementations.

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SOLID Principles

Single Responsibility Principle (SRP)

A class/function should have one reason to change.

Bad:

class UserService {
  createUser(data) { /* creates user */ }
  sendEmail(user) { /* sends email */ }
  generateReport(users) { /* generates report */ }
}

Good:

class UserService {
  createUser(data) { /* creates user */ }
}
class EmailService {
  sendEmail(user) { /* sends email */ }
}
class ReportService {
  generateReport(users) { /* generates report */ }
}

Open/Closed Principle (OCP)

Open for extension, closed for modification.

Bad: Adding new payment types requires modifying existing code

function processPayment(type, amount) {
  if (type === 'credit') { /* ... */ }
  else if (type === 'debit') { /* ... */ }
  // Must modify to add new types
}

Good: New payment types can be added without modification

interface PaymentProcessor {
  process(amount: number): Promise<void>;
}
class CreditProcessor implements PaymentProcessor { /* ... */ }
class DebitProcessor implements PaymentProcessor { /* ... */ }

Liskov Substitution Principle (LSP)

Subtypes must be substitutable for their base types.

Bad:

class Bird {
  fly() { /* ... */ }
}
class Penguin extends Bird {
  fly() { throw new Error("Can't fly!"); } // Violates LSP
}

Good:

class Bird { /* ... */ }
class FlyingBird extends Bird {
  fly() { /* ... */ }
}
class Penguin extends Bird { /* no fly method */ }

Interface Segregation Principle (ISP)

Clients shouldn't depend on interfaces they don't use.

Bad:

interface Worker {
  work(): void;
  eat(): void;
  sleep(): void;
}

Good:

interface Workable { work(): void; }
interface Eatable { eat(): void; }
interface Sleepable { sleep(): void; }