Deno is slow, and why association fallacy matters

False marketing

A common logical fallacy is the Association fallacy — Rust is hyped and proven to be fast and reliable — Deno is written to some small degree in Rust; therefore it has to be fast, as Rust is! Nope — it still can’t even beat Node.js.

Association fallacy — B is not C even though A is B and A is C.

This marketing trick was used extensively for Node.js as well — back in 2010, Node.js was heavily marketed as “a C++ server” in the same way as Deno is now marketed as “a Rust server” by name dropping popular Rust tech as arguments for performance:

Hey look! It has to be fast because it touches both Rust and C++ projects!

The updated numbers

I do verification of performance regularly. Here are numbers from May 2022:

We see that even though Deno is “built on the fastest server technologies available”, it still does not perform significantly better than vanilla Node.js, and certainly not close to optimizations for Node.js. Heck, for WebSockets there are obvious performance problems still in Deno 1.32.

Remember; only performance numbers themselves say anything valid about performance.

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