[specialist]

> 1 real copy of each dependency version...

npm showed me that I lack creativity, for I could not imagine anything worse than maven.

The ~/organization/project/release dir structure is the ONE detail maven got right. (This is the norm, the Obviously Correct Answer[tm], right?)

And npm just did whatever. Duplicate copies of dependencies. Because reasons.

[fiddlerwoaroof]

Node is doing the right thing: if two dependencies in maven have conflicting dependencies, maven just picks an arbitrary one as _the_ version, which results in running with an untested version of your dependency (the dependency is actually depending on a version the developers of that dependency didn’t specify). Because node allows the same dependency to be included multiple times, npm and friends can make sure that every dependency has the right version of its dependencies.

[lhorie]

> Node is doing the right thing

Node does a different thing. It can coalesce two different versions into one if the two things are within a certain semver range, but there's nothing that enforces whether things within a semver range are actually compatible. The most prominent example is Typescript, which famously does not follow semver. Another notable example of how NPM itself does things wrong is that it considers anything in the `^0.x` range as compatible, whereas semver distinctly says the 0.x range is "anything goes".

[deckard1]

Incompatible libs, you say? Try this one on: once upon a time a handful of years ago a package-lock.json I worked on drifted so far from package.json that you could not remove package-lock.json and rebuild purely from package.json. The versions specified in the package.json were incompatible with each other, but the package-lock.json had somehow locked itself to a certain permutation of versions that it somehow just worked.

I always shudder to think that different versions of packages live in node_modules and one library produces an object that somehow makes it to the other version of the library and... I'd rather not think of all these implications or I would go crazy.

[fiddlerwoaroof]

I agree another the 0.x thing. The rest is basically a result of people refusing to use the versioning system the way it’s designed to be used, which is a problem with a package not with the specified behavior of npm here: violating the rules of semver is UB

[lhorie]

I would definitely put part of the blame on the design of the system. It allows anyone to write stuff like `"lodash": "*"`, which is a perfectly valid range as far as semver goes. And then there's things like yarn resolutions, where a consumer can completely disregard what a library specifies as its dependencies and override that version with whatever version they want. And there's aliases (`"lodash": "npm:anotherpackage@whatever"`) and github shorthands and all sorts of other wonky obscure features. And we haven't even touched on supply chain vulns...

[CraigJPerry]

>> maven just picks an arbitrary one as _the_ version

No that’s never been the case. If you have conflicting versions of a dependency in your dependency graph, maven chooses the “nearest neighbour” version - it selects the version specified least far away from your project in the transitive dependencies graph.

Pinning a particular choice is easy too - you just declare the dependency and specify the version you want instead of relying on transitive deps.

[fiddlerwoaroof]

This is what I mean by an arbitrary version: it’s not determined by the dependency but by some characteristic of the dependency tree. And, this is only necessary because the JVM can’t load two versions of the same dependency (ignoring tricks like the maven-shade-plugin)

[kaba0]

The JVM can load the same class any number of times through different class loaders -> only the (class, classloader) tuple has to be unique.

I guess the reason they didn’t went the duplicative direction is that java has safe class loading semantics at runtime and due to valuing storage/memory capacity (which was frankly a sane choice, like 10x bigger java projects compile faster than a js project that pretty much just copies shit from one place to another?)