Jan Kassens
Software Engineer at Facebook
New York, New York, United States
Summary
🤩
Rockstar🎓
Top SchoolJan Kassens is a seasoned software engineer with 17 years of experience, based in New York and a long-tenured frontend engineer at Facebook since 2012. He combines deep React and React Native expertise with full-stack and backend contributions across high-profile open-source projects like React, Relay, GraphQL, and Watchman. His work often focuses on reliability, maintainability, and performance—fixing tricky UI bugs, improving code generation and Flow types, and hardening build and test tooling. Experienced across JavaScript, Rust clients, and mobile/web integrations, he’s comfortable moving between component-level fixes and compiler-level improvements. A detail-oriented contributor, he has a track record of addressing subtle issues (e.g., string refs, re-renders, ASCII portability) that reduce technical debt and keep large codebases healthy.
18 years of coding experience
Technischen Universität Darmstadt
Github Skills (48)
babel610
javascript10
lib10
react-native10
flow-control10
mobile-development10
testing10
component-development10
work-flow10
ui-design10
io10
wpgraphql10
mootools10
typer10
relayer10
Programming languages (14)
Github contributions (5)
relayjs/relay-examples
Aug 2017 - May 2022
A collection of sample Relay applications
Role in this project:
Full-stack Developer
Full-stack DeveloperContributions:105 commits, 89 PRs, 98 pushes in 4 years 8 months
Contributions summary:Jan primarily focused on improving and maintaining the example Relay applications. Their contributions included removing debugging tools and leftover comments. They also upgraded dependencies such as express and graphql, and webpack. Furthermore, the user addressed minor issues and refactored the codebase.
reactrelayrelay-moderngraphql
facebook/relay
Aug 2015 - Oct 2022
Relay is a JavaScript framework for building data-driven React applications.
Role in this project:Full-stack Developer
Full-stack DeveloperContributions:4 releases, 8 reviews, 1639 commits in 7 years 2 months
Contributions summary:Jan primarily contributed to the Relay framework, implementing features related to code generation, particularly around type generation and handling. They worked on features to enhance the functionality of GraphQL through features such as support for raw response types, modules with match annotations, and improving Flow type generation for fragments. Their work involved changes across multiple parts of the compiler, including refactoring and improvements to support a more streamlined code generation process.
javascript-frameworkreact-applications
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