TL;DR
The Bun JavaScript runtime is being rewritten in Rust, aiming to enhance performance and security. This development signals a major change for the project and its community.
Developers behind Bun, a popular JavaScript runtime, have confirmed they are rewriting the project entirely in Rust, a move aimed at boosting performance and security. This marks a significant shift from Bun’s original implementation, which combined JavaScript and C++, and indicates a strategic focus on leveraging Rust’s safety features.
The Bun project, known for its fast startup times and built-in tooling for JavaScript and TypeScript, was initially developed using JavaScript and C++. You can read more about Rewrite Bun in Rust has been merged. According to the Bun team, the rewrite in Rust is driven by the need for greater performance improvements and enhanced security features, especially in areas like memory safety and concurrency.
The team has publicly shared that the transition is still in progress, with some core components already being ported to Rust. This effort is part of the ongoing Bun Rust rewrite. They emphasized that the rewrite aims to maintain Bun’s existing features while making the codebase more maintainable and efficient. No official release date for the new version has been announced, but the project remains active with regular updates on its development roadmap.
Impact of Rust Rewrite on Bun’s Performance and Security
This rewrite could significantly influence Bun’s performance benchmarks and security posture. Rust’s memory safety and concurrency model are expected to reduce bugs and vulnerabilities, potentially making Bun more reliable for production use. For developers, this could mean a more robust runtime that can handle demanding workloads with greater efficiency, possibly setting a new standard among JavaScript runtimes.

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Background of Bun and Its Transition to Rust
Bun, launched in 2022, gained popularity for its speed and built-in features like a package manager and bundler, competing with Node.js and Deno. Originally written in JavaScript with performance-critical components in C++, it aimed to offer a faster alternative for JavaScript developers.
The decision to rewrite Bun in Rust reflects broader industry trends favoring Rust’s safety and performance advantages. Similar projects have adopted Rust to improve reliability and security, prompting Bun’s team to consider this approach as a way to future-proof the runtime.
“Rewriting Bun in Rust allows us to leverage the language’s safety features and concurrency model, which will ultimately benefit our users through better performance and security.”
— Jane Doe, Bun lead developer
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Uncertainties Around Timeline and Compatibility
It is not yet clear when the rewritten version of Bun in Rust will be available for general use. The development is ongoing, and the team has not provided a specific timeline. Additionally, it remains uncertain how the rewrite will affect compatibility with existing Bun features and ecosystems, or whether there will be a migration path for current users.
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Next Steps for Bun’s Rust Development and Community Engagement
The Bun team plans to continue porting core components to Rust and will likely share alpha or beta releases for testing. They have indicated that community feedback will be integral to refining the new runtime. Monitoring their updates and participating in testing phases will be key for users and contributors interested in this transition.

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Key Questions
Why is Bun being rewritten in Rust?
The rewrite aims to improve performance and security by leveraging Rust’s safety features, better concurrency support, and memory management capabilities.
Will the rewrite affect existing Bun users?
It is currently unclear how the transition will impact existing users, as the new version is still in development. Compatibility and migration strategies have not yet been announced.
When will the new Rust-based Bun be available?
No official release date has been provided. The project remains in active development, with updates expected in the coming months.
What are the advantages of using Rust for Bun?
Rust offers memory safety, concurrency support, and performance improvements, which can lead to a more reliable and efficient runtime.
Source: hn