Dan Abramov's "React for Two Computers" explores using React to build a collaborative interface between two physically separate computers. He demonstrates a simplified approach involving manual synchronization of component state between browsers using server-sent events (SSE). By sending state updates over a server as they happen, both clients maintain a consistent view. This method, while not scalable for numerous clients, offers a practical illustration of the core principles behind real-time collaboration and serves as a conceptual foundation for understanding more complex solutions involving Conflict-free Replicated Data Types (CRDTs) or operational transforms. The post focuses on pedagogical clarity, prioritizing simplicity over production-ready implementation.
Dan Abramov's blog post, "React for Two Computers," explores the conceptual underpinnings of React's rendering model and how it could theoretically be extended beyond a single machine. He begins by establishing the fundamental principle of React: declarative descriptions of the User Interface (UI). This means developers describe what they want the UI to look like given certain data, rather than how to achieve that appearance through imperative instructions. React then takes this declarative description and manages the actual DOM manipulations necessary to bring it to life on the screen.
Abramov then introduces the idea of decoupling the two core aspects of React's operation: the rendering of components into a tree-like representation and the subsequent realization of that tree in the browser's Document Object Model (DOM). He proposes a hypothetical scenario where the rendering process, the creation of this "React tree," could occur on a separate computer entirely. This separate machine, dubbed the "server," would perform the computations necessary to construct the React element tree.
The central challenge in this "two computer" model becomes efficiently communicating the changes in the React tree from the server to the client, the computer displaying the UI. A naive approach of sending the entire tree every time a change occurs is deemed inefficient, especially for large and complex applications. Abramov then delves into the strategies React employs to optimize updates, specifically highlighting the concept of "reconciliation."
Reconciliation is the process by which React compares the previous and current versions of the component tree to identify the minimal set of changes needed in the actual DOM. Abramov explains how this same principle could be applied in the two-computer scenario. Instead of transmitting the entire updated tree, the server could calculate the difference, a "diff," between the old and new trees and send only this diff to the client. The client, having a copy of the previous tree, could then apply the diff and efficiently update the DOM, reflecting the changes made on the server.
He further elaborates on the complexities of this diffing process, explaining that simply comparing the tree structures isn't sufficient. The server needs to transmit not only structural changes like adding or removing elements, but also changes in the properties of existing elements. This necessitates a mechanism for serializing and deserializing the React elements and their properties for transmission across the network.
Abramov concludes by acknowledging that this "React for Two Computers" concept is largely a thought experiment, a way to explore the core ideas behind React's architecture and potential future directions. While he doesn't advocate for actually implementing React in this distributed manner in typical scenarios, he suggests that exploring these concepts can lead to a deeper understanding of how React works and how its principles might be applied in other contexts, particularly in optimizing rendering performance and managing complex UI updates. He underscores that the fundamental power of React lies in its declarative approach, which allows for flexibility in where and how the rendering process takes place.
Summary of Comments ( 0 )
https://news.ycombinator.com/item?id=43631004
Hacker News users generally praised the article for its clear explanation of a complex topic (distributed systems/shared state). Several commenters appreciated the novelty and educational value of the thought experiment, highlighting how it simplifies the core concepts of distributed systems. Some pointed out potential real-world applications, like collaborative editing and multi-player games. A few discussed the limitations of the example and offered alternative approaches or expansions on the ideas presented, such as using WebRTC data channels or CRDTs. One commenter mentioned potential security concerns related to open ports.
The Hacker News post titled "React for Two Computers" (https://news.ycombinator.com/item?id=43631004) discussing Dan Abramov's blog post about a hypothetical React-like library for two computers sparked a fairly active discussion with a variety of perspectives.
Several commenters expressed appreciation for the thought experiment and the way it highlighted fundamental concepts of reactivity and data flow. One user described it as "a great way to explain reactivity," and another found it "a very insightful mental model." The simplified, two-computer scenario resonated with some as a clearer way to understand the principles behind React's more complex implementation.
A recurring theme in the comments was the comparison to existing technologies and paradigms. Some pointed out similarities to distributed systems concepts like message passing and eventual consistency. Others drew parallels to functional reactive programming (FRP) and how this two-computer model mirrors some of its core ideas. One commenter mentioned the similarity to the "Actor model," where independent units of computation communicate via messages.
Several commenters delved into the practical implications and limitations of such a system. Discussions arose around the challenges of handling latency, network partitions, and data consistency in a real-world distributed environment. One user highlighted the complexity of dealing with conflicting updates and the need for conflict resolution mechanisms. Another pointed out the performance overhead associated with serialization and deserialization of data.
The hypothetical nature of the blog post also led to discussions about potential use cases and extensions. One commenter speculated on the possibility of applying similar principles to multi-core processors or even within a single application to manage state across different components. Another user suggested exploring the use of CRDTs (Conflict-free Replicated Data Types) to simplify data synchronization.
A few commenters also offered alternative approaches or pointed out existing libraries that address similar problems. Mentions were made of libraries like RxJS and MobX, and concepts like "observables" and "data binding."
Overall, the comments section reflects a positive reception of the blog post, with many users finding it intellectually stimulating and insightful. The discussion ranged from appreciating the pedagogical value of the thought experiment to exploring its practical implications and connections to existing technologies. The comments demonstrate a strong understanding of the underlying concepts and a willingness to engage in thoughtful discussion about the potential and challenges of applying React-like principles to distributed systems.