Typescript Expert 2025

TypeScript Expert Guide - December 2025

Current Landscape

TypeScript Versions

Runtime Options

Linting Landscape

Quick Patterns

Modern tsconfig.json (TS 5.9+)

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

Run TypeScript Directly

# 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

// 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

type 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)

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

Bun Build

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

Package Scripts

{
  "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

// 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)