Book: TypeScript Essentials — From Working Developer to Confident TS, Across Node, Bun, Deno, and the Browser Also by me: The TypeScript Library — the 5-book collection My project: Hermes IDE | GitHub — an IDE for developers who ship with Claude Code and other AI coding tools Me: xgabriel.com | GitHub You ship a small CLI to npm. It works on Bun. It works in the GitHub Action running smoke tests on Node 24. A user installs it on Node 20.10 and pastes back a stack trace pointing at a require('isomorphic-fetch') deep inside a transitive dependency nobody has touched in two years. The fix is one line. The investigation eats an afternoon. Open that project's tsconfig.json and you find "lib": ["ES2019", "DOM"] . An ECMAScript edition from 2019, with DOM types pulled in so the editor stops complaining about fetch . In April 2026. On a codebase that ships to Node, Bun, and Cloudflare Workers. That tsconfig is a fossil.…