Conda unifies by using a sat solver to find versions of software which are mutually compatible regardless of whether they agree on the meaning of semver. So, both approaches require unifying versions. Linking against C gets pretty broken without this.

The issue I was referring to is that in Javascript, you can write code which uses multiple versions of the same library which are mutually incompatible. Since they're mutually incompatible, no sat-solve or unifyer is going to help you. You must permit multiple versions of the same library in the same environment. So far, my approach of ignoring some Javascript libraries has worked for my backend development. :)

Rust does permit multiple incompatible versions of the same library in the same environment. The types/objects from one version are distinct from the types/objects of the other, it's a type error to try mix them.

But you can use two versions of the same library in your project; I've done it by giving one of them a different name.