Worked on the expressjs/express repository to address a bug in HTTP header handling within the res.send method, specifically ensuring that the Content-Length header is only emitted when the Transfer-Encoding header is absent. This targeted backend fix involved updating the Node.js codebase using JavaScript, with a focus on maintaining API stability and preventing header conflicts. Comprehensive tests were added to cover various Transfer-Encoding scenarios, and documentation was updated to reflect these changes. The work demonstrated careful attention to robust testing, clear commit messaging, and precise documentation, contributing to the overall resilience and maintainability of the Express API’s response handling.