Worked on modernizing the build system for the epam/ketcher repository, focusing on upgrading the core to TypeScript 6 and migrating Rollup configurations to .mjs for improved compatibility with Vite 8. The approach involved updating type definitions, refining test and CI configurations, and ensuring stability across ketcher-core and related modules. JavaScript and React were used alongside TypeScript and Rollup to streamline the build pipeline and support future upgrades. The work included targeted fixes after merges, dependency cleanups, and collaboration on tooling enhancements, laying a foundation for ongoing modernization and maintaining release velocity without introducing new bugs during the transition.