Yarr was originally developed for use with Relay (formally Relay Modern) in September 2020 for internal use at Contra. It's since been open-sourced to give back

Yarr was originally developed for use with Relay (formally Relay Modern) in September 2020 for internal use at Contra. It's since been open-sourced to give back to the community and promote Relay adoption. Yarr is the only routing framework that was built from the ground up with the goal of enabling the render-as-you-fetch concurrent UI pattern. It allows code preloading and data preloading. This behavior is enabled even without opt-in to React's experimental Concurrent Mode. Yarr was primarily architected by Eric Taylor, our super talented engineer, and it captures almost 2 years of our experience working with Relay and evolving render-as-you-fetch pattern. It's already in use in production at https://contra.com/ https://contra.com/