Hermes vs QuickJS: What are the differences?

Introduction

Hermes and QuickJS are both JavaScript engines that can be used in various applications, but they have key differences that set them apart.

1. Memory Efficiency: Hermes is known for its reduced memory footprint compared to QuickJS. It achieves this through a compact garbage collector and bytecode representation of JavaScript code, which reduces the amount of memory required for execution. QuickJS, on the other hand, focuses on speed and includes a more traditional garbage collector, which can lead to higher memory usage.

2. Performance: QuickJS places a strong emphasis on performance, aiming to execute JavaScript code as fast as possible. It achieves this through a combination of techniques such as just-in-time (JIT) compilation and aggressive optimizations. Hermes, while also performant, prioritizes memory efficiency, which can result in slightly slower execution speed compared to QuickJS.

3. Integration with React Native: Hermes was specifically designed for use with React Native, providing enhanced performance and startup time for mobile apps. It includes features like ahead-of-time (AOT) compilation and a more efficient bridge between JavaScript and native code. QuickJS, on the other hand, is a standalone JavaScript engine that can be integrated into a variety of environments, making it more versatile but without the same optimizations for React Native.

4. Compatibility and Language Features: QuickJS offers excellent compatibility with the ECMAScript specification and supports a wide range of language features, including recent additions like async/await and generators. Hermes, while also compatible with the specification, has a more limited set of language features, prioritizing memory efficiency over comprehensive language support.

5. Community and Support: QuickJS benefits from a large and active community, with ongoing development and frequent updates. This ensures a robust ecosystem of libraries, tools, and resources. Hermes, while actively maintained by Facebook, has a smaller community and may have fewer third-party resources available.

6. Code Size: QuickJS has a smaller code footprint compared to Hermes, making it easier to embed in resource-constrained environments. This can be advantageous in scenarios where minimizing the overall application size is a priority.

Summary

In summary, Hermes and QuickJS differ in terms of memory efficiency, performance, integration with React Native, compatibility and language features, community and support, and code size. While Hermes prioritizes memory efficiency and is well-suited for React Native applications, QuickJS focuses on performance and offers a wider range of language features.