---

name: typescript-expert-2025 description: Expert TypeScript development patterns and tooling for December 2025. Use when (1) Setting up modern TypeScript projects with Bun, Node 22+, or Deno, (2) Configuring tsconfig, ESM/CJS dual publishing, or build tooling, (3) Implementing advanced type patterns like satisfies, as const, template literals, mapped types, (4) Choosing between Biome, Oxlint, or ESLint for linting, (5) Optimizing TypeScript performance, or any expert-level TypeScript architecture questions.

TypeScript Expert Guide - December 2025

Current Landscape

TypeScript Versions

Runtime Options

Linting Landscape

Quick Patterns

Modern tsconfig.json (TS 5.9+)

Copy{
  "compilerOptions": {
    "target": "ESNext",
    "module": "NodeNext",
    "moduleResolution": "NodeNext",
    "strict": true,
    "noEmit": true,
    "isolatedModules": true,
    "esModuleInterop": true,
    "skipLibCheck": true,
    "declaration": true,
    "declarationMap": true
  }
}

Run TypeScript Directly

Copy# Node 22+ (native)
node --experimental-strip-types app.ts

# Bun (zero config)
bun app.ts

# tsx (Node + esbuild)
npx tsx app.ts

Type-Safe Object Definition

Copy// satisfies: validate type while preserving literal inference
const config = {
  port: 3000,
  env: 'production',
} satisfies { port: number; env: string };
// config.env is 'production', not string

// as const: immutable literals
const routes = ['/', '/api', '/admin'] as const;
// routes[0] is '/', not string

Template Literal Types

Copytype EventName = 'click' | 'hover' | 'scroll';
type Handler = `on${Capitalize<EventName>}`;
// 'onClick' | 'onHover' | 'onScroll'

type Route = `/api/${string}/${'get' | 'post'}`;
// '/api/users/get' | '/api/users/post' | ...

Reference Files

Load based on task:

• TS 5.5-5.9 features & TS 7 preview: See typescript-5x-features.md
• Bun, tsx, tsup, Node 22: See modern-tooling.md
• Advanced type patterns: See advanced-types.md
• Biome, Oxlint, ESLint: See linting-formatting.md
• tsconfig, package.json, ESM/CJS: See project-setup.md
• Zod, error handling, async: See runtime-patterns.md

Build Tool Quick Reference

tsup (Library Bundling)

Copytsup src/index.ts --format esm,cjs --dts

Bun Build

Copybun build ./src/index.ts --outdir ./dist --target node

Package Scripts

Copy{
  "scripts": {
    "dev": "bun --watch src/index.ts",
    "build": "tsup src/index.ts --format esm,cjs --dts",
    "lint": "biome check .",
    "typecheck": "tsc --noEmit"
  }
}

Key Compiler Flags (TS 5.8+)

Utility Types Quick Reference

Copy// Built-in
Partial<T>           // All optional
Required<T>          // All required
Readonly<T>          // All readonly
Pick<T, K>           // Select keys
Omit<T, K>           // Exclude keys
Record<K, V>         // Key-value map
Extract<T, U>        // Filter union
Exclude<T, U>        // Remove from union
NonNullable<T>       // Remove null/undefined
ReturnType<T>        // Function return type
Parameters<T>        // Function parameters
Awaited<T>           // Unwrap Promise

// String manipulation
Uppercase<S>
Lowercase<S>
Capitalize<S>
Uncapitalize<S>

Decision Framework

Runtime Choice

• Bun: New projects, maximum speed, all-in-one
• Node 22+: Production, ecosystem compatibility
• tsx: Existing Node projects, quick migration

Linter Choice

• Biome: New projects, speed + simplicity
• Oxlint: Speed-critical CI, existing ESLint config
• ESLint: Complex rules, full type-aware linting

Build Tool Choice

• tsup: Library publishing, ESM/CJS dual
• Bun build: Bun-native projects
• tsc: Type-checking only (use with bundler)