Swe Programming Typescript

---
name: swe-programming-typescript
description: TypeScript coding standards from authoritative docs/explanation/software-engineering/programming-languages/typescript/ documentation
---

# TypeScript Coding Standards

## Purpose

Progressive disclosure of TypeScript coding standards for agents writing TypeScript code.

**Authoritative Source**: [docs/explanation/software-engineering/programming-languages/typescript/README.md](../../../docs/explanation/software-engineering/programming-languages/typescript/README.md)

**Usage**: Auto-loaded for agents when writing TypeScript code. Provides quick reference to idioms, best practices, and antipatterns.

## Quick Standards Reference

### Naming Conventions

**Types and Interfaces**: PascalCase

- Types: `UserAccount`, `PaymentDetails`
- Interfaces: `IPaymentProcessor` or `PaymentProcessor` (no prefix preferred)
- Type aliases: `type UserId = string`

**Functions and Variables**: camelCase

- Functions: `calculateTotal()`, `findUserById()`
- Variables: `userName`, `totalAmount`
- Constants: `UPPER_SNAKE_CASE` (`MAX_RETRIES`, `API_ENDPOINT`)

**Files**: kebab-case

- `user-account.ts`, `payment-processor.ts`

### Modern TypeScript Features

**Type Inference**: Let TypeScript infer when obvious

```typescript
const name = "John"; // string inferred
const count = 42; // number inferred
```

**Union Types**: Use for multiple possible types

```typescript
type Result = Success | Error;
type Status = "pending" | "completed" | "failed";
```

**Type Guards**: Use for type narrowing

```typescript
function isString(value: unknown): value is string {
  return typeof value === "string";
}
```

**Generics**: Use for reusable type-safe code

```typescript
function identity<T>(value: T): T {
  return value;
}
```

**Utility Types**: Leverage built-in utilities

- `Partial<T>`: Make all properties optional
- `Pick<T, K>`: Select specific properties
- `Omit<T, K>`: Remove specific properties
- `Readonly<T>`: Make all properties readonly

### Error Handling

**Result Pattern**: Prefer over throwing exceptions

```typescript
type Result<T, E> = { ok: true; value: T } | { ok: false; error: E };
```

**Error Types**: Define specific error types

```typescript
class ValidationError extends Error {
  constructor(
    public field: string,
    message: string,
  ) {
    super(message);
    this.name = "ValidationError";
  }
}
```

### Testing Standards

**Jest/Vitest**: Primary testing frameworks

- `describe()` for test suites
- `it()` or `test()` for individual tests
- `beforeEach()`, `afterEach()` for setup

**Type-safe Tests**: Ensure tests are type-checked

```typescript
it("should return user", () => {
  const user: User = findUser("123");
  expect(user.name).toBe("John");
});
```

### Security Practices

**No `any`**: Avoid `any` type

- Use `unknown` for truly unknown types
- Use generics for flexible typing

**Input Validation**: Validate external data

- Use Zod or similar for runtime validation
- Validate before processing

**XSS Prevention**: Sanitize user input

- Use framework escaping (React, Angular)
- Never use `dangerouslySetInnerHTML` without sanitization

## Comprehensive Documentation

For detailed guidance, refer to:

- **[Idioms](../../../docs/explanation/software-engineering/programming-languages/typescript/idioms.md)** - TypeScript-specific patterns
- **[Best Practices](../../../docs/explanation/software-engineering/programming-languages/typescript/best-practices.md)** - Clean code standards
- **[Anti-Patterns](../../../docs/explanation/software-engineering/programming-languages/typescript/anti-patterns.md)** - Common mistakes

## Related Skills

- docs-applying-content-quality
- repo-practicing-trunk-based-development

## References

- [TypeScript README](../../../docs/explanation/software-engineering/programming-languages/typescript/README.md)
- [Functional Programming](../../../repo-governance/development/pattern/functional-programming.md)