Aiden Bai's 'bippy' package is a toolkit that allows developers to access and manipulate the internal workings of React, specifically the fiber tree, which is typically inaccessible.

The package is designed to provide unprecedented access to React internals, offering utility functions that simplify the complex fiber tree structure and enable developers to observe and interact with component props, state, and context across React versions 17-19. This capability allows for advanced debugging, performance analysis, and the creation of specialized developer tools, as exemplified by its use in react-scan for visualizing component renders.

However, Bai issues a strong warning regarding its use:

"⚠️⚠️⚠️ this project may break production apps and cause unexpected behavior ⚠️⚠️⚠️ this project uses react internals, which can change at any time. it is not recommended to depend on internals unless you really, really have to."

The package's ability to override internal handlers also allows for advanced control over features like Hot Module Replacement (HMR). HMR is a development-time feature that enables modules to be exchanged, added, or removed without a full page reload, significantly speeding up development by preserving application state and instantly applying code changes. By intercepting the internal mechanisms that trigger HMR updates, bippy can potentially stop or modify these updates, offering developers granular control over the development refresh cycle.

Aiden Bai, also known for his work on Million.js and React Scan, emphasizes that while bippy offers powerful capabilities for understanding and manipulating React's core, it should be used with extreme caution due to its reliance on unstable internal APIs that can change without notice, potentially leading to application instability or breakage.