language-patterns

Language Patterns

This skill provides language-specific patterns and best practices. Apply patterns that match the project's language and framework.

---

TypeScript Patterns

Type Safety

Use strict types over any:

// Bad
function process(data: any): any {
  return data.value;
}

// Good
interface DataItem {
  value: string;
  count: number;
}

function process(data: DataItem): string {
  return data.value;
}

Use discriminated unions for variants:

type Result<T> =
  | { success: true; data: T }
  | { success: false; error: Error };

function handleResult<T>(result: Result<T>) {
  if (result.success) {
    // TypeScript knows result.data exists
    console.log(result.data);
  } else {
    // TypeScript knows result.error exists
    console.error(result.error);
  }
}

Use unknown over any for external data:

async function fetchData(): Promise<unknown> {
  const response = await fetch('/api/data');
  return response.json();
}

// Then validate/parse
const data = await fetchData();
if (isValidData(data)) {
  // Now safely typed
}

Null Handling

Use optional chaining and nullish coalescing:

// Optional chaining
const userName = user?.profile?.name;

// Nullish coalescing (only for null/undefined)
const displayName = userName ?? 'Anonymous';

// Combine them
const city = user?.address?.city ?? 'Unknown';

Use type guards:

function isUser(obj: unknown): obj is User {
  return (
    typeof obj === 'object' &&
    obj !== null &&
    'id' in obj &&
    'email' in obj
  );
}

Async Patterns

Prefer async/await over raw promises:

// Good
async function fetchUser(id: string): Promise<User> {
  const response = await fetch(`/api/users/${id}`);
  if (!response.ok) {
    throw new Error(`Failed to fetch user: ${response.status}`);
  }
  return response.json();
}

Handle errors properly:

async function safeOperation(): Promise<Result<Data>> {
  try {
    const data = await riskyOperation();
    return { success: true, data };
  } catch (error) {
    return { success: false, error: error as Error };
  }
}