Microsoft Releases React Native Windows 0.81 with Hermes Debugger

Microsoft has released React Native Windows 0.81, with support for the same Hermes debugger used by mobile versions, but the framework lags behind the Android and iOS releases which are now at 0.83. The framework is used by Microsoft for mobile applications including Outlook and Teams, and on the desktop for part of Office and in its Power Apps low-code development platform. This is in contrast to MAUI (Multi-platform App UI), a .NET cross-platform framework which is promoted to developers but appears to have little internal adoption. Hermes is the default JavaScript engine for React Native and is optimized for fast start-up using ahead-of-time optimization. The new release enables use of React Native DevTools (based on Chrome DevTools) to debug JavaScript in React Native, including breakpoints, variable inspection, profiling, memory snapshots, and component inspection. According to the team, “Windows developers now get the same debugging experience as Android and iOS.” This appears to be not quite the case though, since the network and performance tabs in the DevTools are not yet enabled, but will be when the Windows release reaches 0.83. The new release does include component enhancements including better text handling and improved accessibility. React Native was developed by Meta to enable cross-platform user interfaces using JavaScript, not using a web view, but rendering native widgets. The same React framework code runs in the app as used in web applications, but rendering to native platform views. The result is that developers can share JavaScript code between web and mobile applications without relying on an embedded web browser or giving up a native look and feel. The framework is used by Meta for mobile apps including Facebook and Instagram, and by others including Amazon and Shopify. In 2018, the React Native team began work on a new architecture, including a rendering system called Fabric which performs better than the old bridge between JavaScript and native components. The Windows implementation has also migrated to the new architecture, and this 0.81 release is the last to support the old architecture. An important feature of React Native is its support for native code modules. In the old architecture, developers could use either C++ or C# modules in Windows apps. The new architecture though does not support C#, only C++. “Most React Native for Windows applications and libraries, not to mention React Native for Windows itself, are written in C++ so the team prioritized C++ support first,” say the docs. There are plans to support C# in future but “what exists is not nearly robust enough to support the React Native ecosystem,” according to the team. This is one of several caveats regarding development using React Native for Windows. Another is that third-party support is limited, compared to the more widely used iOS and Android versions. The React Native packages registry shows more than 2,000 packages available for mobile, but only 67 for Windows. Despite those caveats, and the lag in implementing new versions, the future of React Native for Windows is underpinned by Microsoft’s own usage by the Office team. The company said last year that React Native is “critical for Office’s modernization efforts” and that “React Native content islands seamlessly integrate into an app’s overall UI giving a consistent look and feel across an application.” The popularity of JavaScript/TypeScript means that React Native for Windows may be worth a look for developers who need desktop applications as well as mobile. There is a question though: why does Microsoft support two cross-platform frameworks which have a lot in common, since both use high-level languages (JavaScript or C#) and both render native platform widgets? “Why didn’t the Office team use Maui for cross platform?” asked one developer, with no answer yet. The reason may be partly technical, but may also go back to long-standing internal differences between the developer division, and the Windows and Office teams.