1. Missing `node:http2`
2. Missing `node:test`, so it's more difficult to execute the same test files within Bun as we do via Node. I wrote a custom Bun loader to mock parts of `node:test`.
3. Vite and ESLint do not work.
4. Still occasionally segfaults, and it's difficult to find out why/where.
5. Surprisingly, some code runs slower in Bun than in Node. For example, generating JWE with symmetric encryption. But this might be WebCrypto vs OpenSSL.
6. Subtle differences between WebKit and V8 (e.g., how they handle dates).
I am annoyed with the bombastic claims behind bun.
I wasted a day trying to get vite to work when they first announced it. Really excited about not needing >1gb of ram to compile a react project... Boggles my mind that react bundling uses more RAM than compiling linux.
It is still unable compile http://chatcraft.org due to some problem with wasm plugin.
They also said that bunx --bun option was a pre-1.0 workaround, and didn't keep that promise.
Performance-wise their claims are suspect, safari js engine was always better at startup and memory use at the expense of a relatively weak JIT. They paired that up with a ton of stuff reimplemented in native code to make their cli and hello world workflows fast. This means people will be in for a perf surprise when they start bottlenecking in JS hotpaths.
And you're right to be skeptical. With performance, so much depends on your actual code and program-specific bottlenecks. The difference in runtime speed between JSC and V8 is minimal, so a lot of Bun optimization must be in the gaps between your code and the core JS engine or in startup time (e.g., running `bun install` or `bun test`).
In my benchmarks, our actual runtime performance of long-running JS code is ~25% faster under Bun than under Node. However, sometimes Bun is ~25% slower - notably with tasks that require binary processing (e.g, fflate, sharp) or encryption (e.g., jose). We're committed to JS and will be constrained by its performance for a long time, so a "free" 10-30% speed up at runtime is worth the effort, but it's not a 10x slam dunk like the benchmarks on Bun's homepage imply.
