What Bun changed

• Added bun check, a new command for TypeScript type checking that runs 3x to 6.4x faster than tsc.
• Introduced Bun.FetchSession for managing groups of network requests with shared settings.
• Added experimental Bun.ModuleGraph to run multiple app instances in one process.
• Reduced idle server CPU usage by 67–89% and memory usage by 6–11%.
• Added --disallow-code-generation-from-strings to block potentially unsafe functions like eval().
• Upgraded JavaScriptCore to improve JSON.parse speed and general performance.

Bun is moving beyond just running code to managing code quality. By adding a built-in TypeScript type checker that is significantly faster than the official tool, they are making it harder for developers to justify using the standard TypeScript compiler (tsc).

• Updated the latest version from v1.4.1 to v1.4.2.
• Fixed a bug in bun build that broke Elysia apps.
• Fixed a memory leak in AsyncLocalStorage.
• Added support for CMYK JPEG decoding in Bun.Image.
• Upgraded JavaScriptCore to fix issues with dates and arrays.
• Added new instructions for scaffolding React apps using bun init --react.

This update fixes critical regressions that broke specific app frameworks and caused memory issues. It shows the team is moving fast to stabilize the tool after a major release.

• Added HTTP/2 support to the Bun.serve() function.
• Introduced --offline and --prefer-offline flags for the package manager.
• Reduced compiled executable sizes by 45% (example: 376 MB to 207 MB).
• Improved Buffer read and write speeds by up to 9x.
• Added Bun.write() support for streaming response bodies directly to disk.
• Fixed 188 bugs and upgraded the JavaScriptCore engine.
• Added crypto.argon2 support to the native crypto module.

This update focuses on performance and reliability. It adds key networking features like HTTP/2 and offline installs, while significantly reducing the size of compiled apps.