Under the hood: Improving messages

What this post added

The 'mercury project' improved the reliability of Facebook messages and chat by replacing existing implementations with a more robust version. Key technical contributions include adopting a CommonJS-like module system for better JavaScript dependency management, implementing test-oriented development with over 85% test coverage and a focus on unit testing, and embracing functional programming paradigms to build a highly decoupled system capable of fast, incremental loading. This involved replacing OOP patterns with functional ones, modeling domain objects as structured data, and using continuations for asynchronous operations, which simplified caching and allowed initialization and updates to share code paths.