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