As a case study we evaluated the performance of this along with other languages that use immutable data structures (perf testing) for a recent production app we were building. After some evaluation we had the opinion that the penalty of using immutable HAMT's on the Node/JS platform is just too high, at least in its current lib form. Immutable structures are often somewhat slower, but the relative penalty of using a HAMT on the Node/JS platform vs a straight mutable structure was much higher than other languages. Floats for numbers, conversions back and forth implicitly, pop count intrinsic missing, conversions in and out, and other such overheads make the relative penalty of an immutable HAMT vs a mutable JS map much higher compared to other languages such as .NET or Java let alone C/Rust.
Given Node is mostly single threaded as well some of the advantages (not all!) of immutability diminish on that platform making the performance penalty harder to swallow, at least for my use case.
It of course may not matter to your case, but I find the benefits of these structures come from their quicker clone/copy time in many applications, snapshot like characteristics, easy large diff's, etc. For this to matter the collection has to be of a decent size where a linear copy/equals/etc is too slow to work for the use case. At that point speed starts to matter as the costs of random lookup start to grow/drift further away from a standard mutable map and for JS we deemed the penalty too high and decided on another backend platform amenable to writing generic data structures.
Given Node is mostly single threaded as well some of the advantages (not all!) of immutability diminish on that platform making the performance penalty harder to swallow, at least for my use case.
It of course may not matter to your case, but I find the benefits of these structures come from their quicker clone/copy time in many applications, snapshot like characteristics, easy large diff's, etc. For this to matter the collection has to be of a decent size where a linear copy/equals/etc is too slow to work for the use case. At that point speed starts to matter as the costs of random lookup start to grow/drift further away from a standard mutable map and for JS we deemed the penalty too high and decided on another backend platform amenable to writing generic data structures.