name: TypeScript Ecosystem description: This skill should be used when the user asks to "write typescript", "typescript config", "tsconfig", "type definition", "generics", "utility types", or works with TypeScript language patterns and configuration. Provides comprehensive TypeScript ecosystem patterns and best practices.

TypeScript Ecosystem

Core Concepts

• Strict mode: Enable strict: true for maximum type safety
• Module resolution: nodenext for ESM Node.js, bundler for Vite/esbuild/webpack
• Type narrowing: Use type guards (typeof, instanceof, in, custom predicates)
• Utility types: Partial, Required, Pick, Omit, Record, Extract, Exclude, ReturnType, Awaited

Recommended tsconfig

Node.js 22 LTS (ES2023):

{
  "compilerOptions": {
    "target": "ES2023",
    "lib": ["ES2023"],
    "module": "nodenext",
    "moduleResolution": "nodenext",
    "strict": true,
    "esModuleInterop": true,
    "skipLibCheck": true,
    "declaration": true,
    "declarationMap": true,
    "sourceMap": true,
    "outDir": "./dist",
    "rootDir": "./src"
  },
  "include": ["src"],
  "exclude": ["node_modules", "dist"]
}

Key Strict Options

• strictNullChecks - null/undefined handled explicitly
• noImplicitAny - Error on implicit any
• noUncheckedIndexedAccess - Add undefined to index signatures
• noUnusedLocals/Parameters - Error on unused variables

Type Patterns

Conditional Types with infer

type UnwrapPromise<T> = T extends Promise<infer U> ? U : T;
type ArrayElement<T> = T extends (infer E)[] ? E : never;

Mapped Types with Key Remapping

type Getters<T> = {
  [K in keyof T as `get${Capitalize<string & K>}`]: () => T[K];
};

Custom Type Guards

function isCat(pet: Cat | Dog): pet is Cat {
  return (pet as Cat).meow !== undefined;
}

Branded Types

type UserId = string & { readonly __brand: unique symbol };
type OrderId = string & { readonly __brand: unique symbol };

satisfies Operator

const config = {
  endpoint: "/api",
  timeout: 3000,
} satisfies Record<string, string | number>;
// config.endpoint inferred as "/api" (literal), not string

Anti-Patterns

• any abuse: Use unknown and narrow with type guards
• Type assertions: Use type guards instead of excessive as casts
• Enums: Use as const objects instead
• Namespaces: Use ES modules
• Barrel overuse: Can hurt tree-shaking

Tools

• tsc --noEmit - Type check only
• tsx - Run TypeScript directly with esbuild
• ESLint flat config with typescript-eslint
• Vitest or Jest for testing

Context7 Reference

Library ID: /microsoft/typescript