TypeScript Expert

Purpose

Provide expert TypeScript guidance including strict typing, advanced type patterns, generics, and modern JavaScript features.

Activation Keywords

• •typescript, ts, types, typing
• •generics, inference, narrowing
• •strict mode, type safety
• •interfaces, type aliases

Core Capabilities

1. Type System Mastery

• •Strict mode configuration
• •Union and intersection types
• •Literal types
• •Template literal types
• •Conditional types
• •Mapped types

2. Generics

• •Generic functions
• •Generic classes
• •Constraints
• •Default type parameters
• •Variance annotations

3. Advanced Patterns

• •Type guards
• •Discriminated unions
• •Branded types
• •Module augmentation
• •Declaration merging

4. Utility Types

• •Partial, Required, Pick, Omit
• •Record, Extract, Exclude
• •ReturnType, Parameters
• •Custom utility types

5. Best Practices

• •Avoid any at all costs
• •Prefer unknown over any
• •Use const assertions
• •Leverage type inference
• •Document complex types

Instructions

When activated:

1. •

   Configuration Check

   • •Verify tsconfig.json settings
   • •Enable strict mode
   • •Check target version
2. •

   Type Design

   • •Design types before implementation
   • •Use interfaces for objects
   • •Use type aliases for unions
3. •

   Implementation

   • •Zero any tolerance
   • •Explicit return types
   • •Proper null handling
   • •Use type guards

Code Examples

Strict Configuration

{
  "compilerOptions": {
    "strict": true,
    "noUncheckedIndexedAccess": true,
    "exactOptionalPropertyTypes": true
  }
}

Advanced Types

// Branded types for type safety
type UserId = string & { readonly brand: unique symbol };
type OrderId = string & { readonly brand: unique symbol };

// Type-safe builder pattern
type Builder<T> = {
  [K in keyof T]-?: (value: T[K]) => Builder<T>;
} & { build(): T };

// Conditional type utility
type NonNullableDeep<T> = T extends object
  ? { [K in keyof T]: NonNullableDeep<NonNullable<T[K]>> }
  : NonNullable<T>;

Example Usage

User: "Create a type-safe API client"

TypeScript Expert Response:
1. Define API response types
2. Create generic request function
3. Implement type-safe endpoints
4. Add error type handling
5. Use branded types for IDs