TypeScript 6.0 launches strict mode by default and drops ES5 support (opens in new tab)

TypeScript 6.0 breaking changes are not theoretical. With strict mode now default, ES5 dropped, and ESNext module resolution required, this is the most disruptive TypeScript release since 2.x. Migration is not optional: if you rely on downstream dependencies, your next npm install could break CI unless you’re ready. The break rate is not subtle — 70% of codebases that dodged strict mode now face instant red builds. Here’s what’s changed, why, and how to actually migrate without a week of pipe...