5 TypeScript Defaults That Quietly Changed in 2026 (And Why Your Build Is Now Broken)

Book: TypeScript in Production 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 bumped TypeScript from 5.x to 6.0 in a Renovate PR. The PR was green on your laptop. CI was green on a fresh checkout. The diff was four characters in package.json . You merged. Then the deploy queue lit up. > tsc --noEmit src/util/iter.ts:9:5 error TS7034: Variable 'rows