Benefit of FFI in Node?

[SuibianP]

I am finding it hard to understand the very prevalent use of FFI in Node, as opposed to directly targeting N-API or (in the case of a proprietary DLL) a pre-compiled stub.

Statically compiled N-API stubs should have the same ABI stability guarantees without the runtime overhead. FFI defers the compilation of call stub from compile time to either JIT or VM, incurring a nontrivial overhead due to marshalling arguments based on runtime description of target (ffi.ForeignFunction). While this also comes with the flexibility of dynamic signatures, I don’t see how this could be useful in the general case, where the functions to be called are known beforehand and their calling conventions and signatures are fixed up front.

What would be some cases where FFI is superior compared to N-API stub? Why have people been using node-ffi[-(napi|rs)] where a stub would seemingly suffice?

[magic-akari]

Based on my experience, I would generally recommend N-API as the preferred approach for native interactions in Node.js whenever possible. However, there are practical scenarios where solutions like node-ffi or dynamic linking (dlopen) become necessary - often due to non-technical constraints rather than engineering preferences.

Common examples include working with proprietary DLLs where source code isn't available, legacy systems with lost source code, or organizational requirements mandating binary-only distribution. There might also be edge cases I haven't encountered yet, and I'd be grateful to hear about additional use cases from others' experiences.

[SuibianP]

Thanks for the reply!

proprietary DLLs where source code isn't available, legacy systems with lost source code

Please do correct me if I am wrong, but wouldn't it be possible to use a stub to do the dynamic linkage as long as the interface is known? It should even be possible to generate such stub automatically with something like SWIG, although I have not tried.

organizational requirements mandating binary-only distribution

Not sure if I understand this one, given that node addons are just dynamic libraries themselves, which one can argue is more binary-only than node-ffi where the interface is in JS instead.

[SuibianP]

Made some benchmarks with interesting results: https://github.com/SuibianP/node-ffi-benchmark?tab=readme-ov-file#node-ffi-benchmark

[tianxiadys]

If you need to call functionalities not natively supported by Node.js during development, FFI is the solution with the lowest learning curve and maintenance cost. You don't have to set up complex C++ toolchains and IDEs—you can accomplish everything using pure JavaScript.

[tianxiadys]

Not every developer or team possesses C++ expertise. Sometimes, they simply need to call a DLL file from an unknown source, with no C++ specialists available in the team—this scenario is actually quite common.