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TIL Accessing an ESM import variable is 10x slower than CJS because of live bindings

Relative performance of CJS vs ESM · Issue #44186 · nodejs/node

Version v14.20.0, v16.16.0, v18.7.0 Platform Darwin MacBook-Pro-5.localdomain 21.5.0 Darwin Kernel Version 21.5.0: Tue Apr 26 21:08:37 PDT 2022; root:xnu-8020.121.3~4/RELEASE_ARM64_T6000 arm64 Subs...

9:09 PM · Aug 18, 2022

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Tanishq Kancharla (tk)

@moonriseTK

Aug 19, 2022

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@privatenumbr

this is only for classes right?

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OP's benchmarks might be influenced by class concerns, but the slowdown is coming from accessing the ESM variable You can replace the class with a no-op function and get similar results

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in bun it seems to be the same

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and

run with async: true and the results are the opposite

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Possible, but this is optimizable at the engine level. We put in place few invariants that can help, e.g.: accessing these bindings will never throw. It is a matter of pushing implementers to optimize those code paths. That can certainly happen if we start using ESM more in apps.