Under the hood: Improving messages

The 'mercury project' significantly improved the reliability and development process for Facebook messages and chat. Key contributions include: adoption of a CommonJS-like module system to replace a fragile JavaScript dependency management system, leading to better code organization and reduced regressions; emphasis on test-oriented development with over 85% test coverage and a culture of accepting patches only with accompanying tests; and a shift from Object Oriented Programming (OOP) patterns to functional programming, modeling domain objects as structured data rather than class prototypes. This functional approach enables fast, incremental loading and updates, making the system more real-time and easier to cache.