TypeScript Strict Mode Migration

How do I migrate a large codebase to strict mode without breaking everything?

Start with `strictNullChecks: false` and enable strict options one at a time. Fix errors file by file using // @ts-expect-error comments temporarily. Consider using the `typescript-strict-plugin` for gradual adoption.

Which strict option should I enable first?

Start with `noImplicitAny`. It catches the most bugs with the least migration effort. Then move to `strictNullChecks`, which is harder but finds more real bugs.

How do I handle third-party libraries without good types?

Create a `global.d.ts` file for custom declarations. Use `declare module 'library-name'` for untyped libraries. The @types/* packages on npm have community-maintained types for popular libraries.

Is strict mode worth the migration effort?

Yes. Teams consistently report 30-50% fewer runtime errors after enabling strict mode. The upfront cost pays off quickly in reduced debugging time and increased confidence during refactoring.