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27 Jun, 2023 | react native mobile app development services

React Native Hermes: A New Javascript Engine for Faster Performance

React Native Hermes: A New Javascript Engine for Faster Performance
React Native has transformed the creation of mobile apps by enabling developers to develop cross-platform applications from a single codebase. React Native has grown to be a go-to framework for many developers because of its large community and rich component library. Performance, however, becomes increasingly important as applications become more complicated. Facebook released React Native Hermes, a new version that offers improved performance, to alleviate this worry. In this blog post, we will explore the features and benefits of React Native Hermes.

Here is a look at some of the latest features and improvements in React Native versions:

  • Hermes: Hermes is a brand-new JavaScript engine created to boost the efficiency of React Native applications. Although it is still in development, it has already demonstrated notable improvements in startup time, program size, and memory usage.
  • New Architecture: A new architecture in React Native is intended to boost performance and make it simpler to create intricate apps. The new architecture supports more declarative coding and is based on the React Hooks API.
  • New APIs: A number of new APIs in React Native make it simpler to create apps with a native appearance. These APIs come with new elements, stylistic choices, and APIs for interacting with native APIs.
  • Improved Tooling: Recent updates have improved the React Native toolset. This adds enhancements to the testing framework, debugger, and development server.

What is React Native Hermes?

React Native A JavaScript engine designed exclusively for React Native applications is called Hermes. It is intended to speed up startup times, consume less memory, and give users a more reliable and smooth experience. React Native Hermes substitutes its own fast and effective engine for React Native's built-in JavaScript engine (JavaScriptCore). React Native Hermes can help developers create React Native applications with quicker startup times, less memory utilisation, and faster UI interactions.

How Fast is Hermes? 

React Native Hermes is known for its impressive speed and efficiency. By leveraging AOT compilation and static type analysis, it can achieve faster JavaScript execution, resulting in improved overall performance. The exact speed of Hermes can vary depending on various factors, such as the complexity of the application, device specifications, and specific optimizations implemented by the developer. However, in general, Hermes enables React Native applications to start up faster and provide smoother user experiences compared to the default JavaScript Core engine.

Hermes Engine and JavaScript Execution

The Hermes engine is a lightweight and efficient JavaScript engine optimized for mobile devices. It employs various techniques, such as AOT compilation and static type analysis, to deliver superior performance. By compiling JavaScript code ahead of time, Hermes eliminates the need for runtime compilation, resulting in faster startup times. Additionally, Hermes employs a compacting garbage collector that reduces memory fragmentation and improves memory utilization. These optimizations enable Hermes to provide a more consistent and efficient JavaScript execution environment.

Hermes and JavaScript Optimization

Hermes focuses on optimizing JavaScript execution to enhance the overall performance of React Native applications. By leveraging static type analysis, Hermes can make certain performance optimizations that are not possible with traditional JIT compilation engines. This leads to faster JavaScript execution, enabling React Native apps to handle complex operations more efficiently.

Hermes Build and Integration

Integrating Hermes into a React Native project is a straightforward process. To use Hermes, developers need to enable it during the build process by specifying the necessary configuration. Once enabled, the React Native packager compiles the JavaScript code using Hermes, generating optimized bytecode that is ready to be deployed to devices. Existing React Native projects can also be easily migrated to Hermes without significant code changes, making it a convenient option for optimizing performance. react native hermes new version

Key Features of React Native Hermes

  1. Faster Startup Time:

    React Native Hermes' capacity to significantly speed up application starting time is one of its main features. During the building project, Hermes uses an ahead-of-time (AOT) compilation to transform JavaScript code into highly efficient bytecode. As a result, JavaScriptCore no longer requires the normal Just-in-Time (JIT) compilation. The programme launches more quickly as a result, giving users a more responsive experience.
  2. Reduced Memory Usage:

    Mobile devices often have limited resources, including memory. React Native Hermes optimizes memory usage by employing a more efficient garbage collection mechanism. It uses a compacting garbage collector that reorganizes memory to reduce fragmentation and improve overall memory utilization. By reducing the memory footprint, Hermes allows applications to run smoothly even on low-end devices.
  3. Smoother UI Interactions:

    With React Native Hermes, developers can expect smoother and more consistent user interface (UI) interactions. The improved JavaScript engine ensures that UI updates and animations are executed more efficiently, resulting in a better user experience. This is particularly beneficial for complex applications with heavy UI components or animations.
  4. Better JavaScript Performance:

    Hermes leverages static type analysis to optimize JavaScript execution. It can make certain performance optimizations that are not possible with the traditional JIT compilation approach. This results in faster JavaScript execution, enhancing the overall performance of React Native applications.

Benefits of React Native Hermes

  1. Improved User Experience:

    By reducing startup time and memory usage, React Native Hermes provides a significant boost to the user experience. Applications built with Hermes start up faster and respond quickly to user interactions, leading to higher user engagement and satisfaction.
  2. Enhanced Performance on Low-end Devices:

    Mobile devices with limited resources often struggle to handle resource-intensive applications. React Native Hermes is specifically designed to address this issue. By reducing memory usage and optimizing JavaScript execution, Hermes enables smooth performance even on low-end devices, expanding the potential user base for React Native apps.
  3. Increased Development Efficiency:

    Developers may concentrate more on creating features and functionality with React Native Hermes as compared to performance optimisation. Developers may spend more time enhancing the value of their applications and less time on performance optimisation due to the enhanced performance.
  4. Compatibility and Easy Integration:

    React Native Hermes is fully compatible with existing React Native projects. It can be seamlessly integrated into new or existing projects, providing a hassle-free performance boost without requiring significant code changes.
It is important to note that the actual performance gains achieved with Hermes may vary depending on factors such as the complexity of the application, device specifications, and specific optimizations implemented by the developer. It is recommended to benchmark and test the application in various scenarios to assess the performance improvements brought by Hermes.

React 18:

React 18 introduces several new features and improvements aimed at enhancing the developer experience and performance. Some key highlights of React 18 include automatic batching, which optimizes rendering and improves performance, and React Server Components, a new approach to server-rendered components that enables more efficient data fetching and rendering. Additionally, React 18 introduces Concurrent Mode, which allows for smoother user interfaces and better responsiveness by enabling the rendering of components in a non-blocking manner. Overall, React 18 brings significant advancements to React, making it more powerful and efficient for building modern web applications.

React Native 18 New Architecture:

React Native's new architecture, often referred to as "Fabric," is a major reworking of the internals of React Native. It aims to improve performance, stability, and extensibility of React Native applications. The new architecture includes a more efficient threading model, enhanced bridge communication, and better handling of UI components. Fabric provides better control over the rendering pipeline, resulting in smoother animations and improved responsiveness. It also enables more seamless integration with native modules and third-party libraries. The new architecture is designed to make React Native more scalable, adaptable, and capable of handling complex UI interactions, ultimately enhancing the development experience for building cross-platform mobile applications. Benefits of React Native Hermes


For developers looking to improve the performance of their React Native applications, React Native Hermes is a game-changer. Hermes gives developers the tools they need to make high-performing apps that offer a better user experience by placing a great focus on quicker startup times, decreased memory usage, and increased JavaScript performance. Both developers and users gain a great deal from React Native Hermes' efficient resource use and enhanced UI interactions. Hermes should be taken into consideration for any React Native project seeking to attain top performance due to its compatibility and simplicity of integration. Learn how the new Hermes JavaScript engine enhances the speed and efficiency of your applications by exploring our React Native development services. In conclusion, React Native Hermes, with its Hermes engine and AOT compilation capabilities, provides a powerful solution for boosting the performance of React Native applications, delivering faster startup times, reduced memory usage, and smoother user interactions. Developers can explore various blogs and resources to gain deeper insights into the benefits and implementation details of Hermes in React Native projects.

Frequently Asked Questions

What is React Native Hermes?

React Native Hermes is a JavaScript engine developed by Facebook specifically for use with React Native applications. It is designed to improve the startup time, memory usage, and overall performance of React Native apps.

What are the advantages of using React Native Hermes?

Using React Native Hermes can bring several benefits to your React Native app, including faster startup times, reduced memory footprint, improved app performance, and better overall user experience. It achieves these benefits by optimizing the JavaScript execution and garbage collection process.

How does React Native Hermes optimize performance?

React Native Hermes achieves performance optimization by using ahead-of-time (AOT) compilation, which means that the JavaScript code is pre-compiled into an efficient bytecode format during the build process. This eliminates the need for runtime interpretation and improves the app's performance.

Is React Native Hermes compatible with all React Native projects?

React Native Hermes is compatible with most React Native projects. However, it's important to note that certain native modules or third-party libraries might not be fully compatible with Hermes. It's recommended to check the compatibility of your dependencies before adopting Hermes in your project.

How do I enable React Native Hermes in my project?

Enabling React Native Hermes in your project involves a few steps. First, ensure that you have the latest version of React Native installed. Then, follow the instructions provided in the React Native documentation to enable Hermes for your iOS and Android projects. The process may vary depending on your development environment and the version of React Native you are using.

Can I use debugging tools with React Native Hermes?

While React Native Hermes optimizes app performance, it does limit the use of some debugging tools. Debugging options like the React Native Debugger or Chrome DevTools may not work as expected with Hermes. However, you can use console.log statements or the Flipper debugging tool provided by Facebook for debugging purposes.

Can I switch back to the default JavaScript engine if I encounter issues with Hermes?

Yes, if you encounter any compatibility issues or limitations with React Native Hermes, you can switch back to the default JavaScript engine (JSC) or the newer JavaScript engine (V8). React Native provides instructions on how to switch between these engines, allowing you to revert to the default engine if needed.

Is React Native Hermes recommended for all React Native projects?

While React Native Hermes provides performance benefits, it might not be necessary or suitable for every React Native project. It's recommended to evaluate your project's specific requirements and consider factors such as the app's complexity, compatibility with dependencies, and debugging needs before deciding to use React Native Hermes.

What is React 18?

React 18 is the latest major version of the React JavaScript library developed by Facebook. It introduces new features, improvements, and performance enhancements to make building user interfaces more efficient and enjoyable.

What are the key features of React 18?

React 18 introduces several notable features, including Concurrent Mode, which enables smoother rendering and responsiveness, and React Server Components, which allows rendering components on the server. It also includes improvements to the React developer experience, such as Fast Refresh and improved error handling.

Written by Peter

Peter is a Flutter Developer at WEDOWEBAPPS LLC. He follows all the innovative technologies for the mobile world. He also likes sharing his knowledge with the people by mentoring aspiring developers and blogging.