I feel spoiled enough by the ecosystem to expect that libraries which wants/advertises itself to be a standard for Node.js to be backed by native code instead of pure Javascript, especially if the use case is complex, numerical computation.
Aside from that, the collection presented here is actually quite remarkable, kudos to the developer(s).
Re: native vs JS. I'd say it depends. For certain implementations, such as operations on large arrays, native implementations can provide performance benefits (see https://github.com/stdlib-js/stdlib/tree/develop/lib/node_mo...). However, for other implementations, including common mathematical functions, implementing them in pure JavaScript can be more performant when running in Node.js, as you do not need to cross from JS to C/C++ (see https://github.com/stdlib-js/stdlib/tree/develop/lib/node_mo...). Lastly, even if functionality is backed by native code, would still need JavaScript fallbacks in order to, e.g., allow for bundling and use in non-Node.js environments.
Aside from that, the collection presented here is actually quite remarkable, kudos to the developer(s).