"Any type of value as key" is quite misleading since anything other than primitive types (number, bool, string) is compared by reference. Observe:

  > const m = new Map();
  undefined
  > m.set([1], "one");
  Map(1) {Array(1) => "one"}
  >m.get([1])
  undefined

C++ and Rust don't stand for this nonsense. You can't even define a custom hashing function, which means if you want a useful map for anything other than numbers and strings you have to write a wrapper around `Map` that hashes the objects to numbers or strings, and then you're more or less back to raw objects.

It's definitely better than raw objects because it doesn't mix up data and methods, but it's not much better.

I was quite surprised to read that you can't set a custom hasher in C++/Rust, and I even went and made sure that it's possible.

But then I re-read your comment and realized you've meant that you can't do this in JS.

Oh you can, just implement toString and js will use it for hashing

No it won't.

Map, no. Plain object, yes.

It doesn't "use `toString` for hashing", it just converts the key to a string. That is not the same (e.g. you can't recover the original key).

> ES6 has classes

To clarify, I miss having an object model that allows customisation of hashing, equality etc

> ES6 has a Map

Thanks for this; I'll check it out. One simple example of a key that is hard to use strings with is a composite key of 2 strings. OK, you could concatenate them using a character you know won't be used in either string, but what if it's user input? The code is then littered with in/out concatenation/splitting my this extra character etc. (And that's the simple case without other types etc.) It's much easier to have a clear way to customise the hash function IMHO.

Most programming languages have a nice delineation between a dictionary and an object but they are one and the same in JS and that'll throw plenty of traditional programmers for a loop.

To be fair Python has the concept of "everything is a dictionary" running pretty deep in its DNA. To a certain extent everything in Python is syntactic sugar over dictionaries.

Yeah, but that's implementation. Top level syntax, an object and dictionary are distinct.