Worked on the shaka-player repository to address upcoming type-checking issues related to Closure Compiler’s handling of Symbol.iterator. Focused on improving build stability by implementing targeted bug fixes in JavaScript, specifically updating externs and internal iterator implementations to support the Iterable interface. Applied compiler internals expertise to add necessary overrides and annotations, ensuring compatibility with future Closure Compiler checks. The approach emphasized careful refactoring and thorough documentation, reducing the risk of build-time errors and supporting smoother continuous integration. This work enhanced code maintainability and forward-compatibility, demonstrating a strong understanding of type checking and modern JavaScript development practices.