TypeScript Project

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applyTo: "**/*.ts, **/*.tsx"
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# TypeScript Development Instructions (2025)

_Last updated: October 2025_

- Always use the fetch tool to look up the latest TypeScript documentation: https://www.typescriptlang.org/docs
- Use strict mode in tsconfig.json for maximum type safety
- Leverage TypeScript's type system: interfaces, types, generics, utility types
- Avoid using `any` type - use `unknown` when type is truly unknown
- Use type inference when types are obvious, explicit types when clarity is needed
- Implement proper type guards for runtime type checking

**Core Principles:**

- Use interfaces for object shapes and contracts
- Use type aliases for unions, intersections, and complex types
- Implement generics for reusable, type-safe code
- Use const assertions for literal types
- Leverage utility types: Partial, Pick, Omit, Record, Readonly
- Use discriminated unions for type-safe state machines

**Type Safety:**

- Enable strict null checks (strictNullChecks: true)
- Use optional chaining (?.) and nullish coalescing (??)
- Implement type guards (typeof, instanceof, custom guards)
- Use assertion functions for runtime validation
- Avoid type assertions (as) unless absolutely necessary

**Advanced Patterns:**

- Use mapped types for transforming types
- Implement conditional types for type-level logic
- Use template literal types for string manipulation
- Leverage const type parameters (TypeScript 5.0+)
- Use satisfies operator for type validation without widening

**Configuration:**

- Configure tsconfig.json properly for your project type
- Use path mapping for clean imports
- Enable noUncheckedIndexedAccess for safer array access
- Use composite projects for monorepos

**Summary:**

> For all TypeScript work, always use the fetch tool to look up the latest documentation from https://www.typescriptlang.org/docs. Write type-safe, maintainable code with strict TypeScript.