npm vs pnpm explained (engineering prep)

Added: 2026-05-29

[00:00:00]In today's interview, I want you to explain the difference between NPM and PNPM. If you can't do this, you won't get the job. Well, every Node project copies all its dependencies into a Node modules folder. So, if you've got 50 projects on your laptop, that is 50 copies of React.

[00:00:13]>> Okay, and PNPM fixes that?

[00:00:15]>> PNPM keeps one copy in a global warehouse, and every project just links to it. Just links to it like a symlink?

[00:00:21]There's actually two kinds, and the first of which is hard links. PNPM keeps a global warehouse on your laptop with one shelf, which is basically just a folder on a disk per package version.

[00:00:31]When you install React in a project, PNPM doesn't copy the React files in. It just points your project's Node modules to the React shelf. It's the same file, and no extra disk needed.

[00:00:40]>> And the second kind? Second is symbolic links or symlinks. Those build the dependency tree itself. If React needs Lodash, PNPM drops a symlink in the React folder pointing at the Lodash shelf in the warehouse, and it uses the same trick for every dependency. The whole tree gets stitched together out of symlinks pointing at shelves. Okay, so should I use NPM or PNPM?

[00:00:59]>> Well, for anything serious, I'd recommend PNPM. One of the main reasons is also no more phantom dependencies.

[00:01:04]>> Phantom dependencies? With NPM, every package gets dumped flat at the top of your Node modules. So, your code can import Lodash even when it's not in your package.json. That is, as long as something else pulls it in. It works on your laptop, and then it breaks the day that something else gets removed and someone deploys it. All right, so the bug shows up at install time rather than at 2:00 a.m. in prod.

[00:01:23]>> Exactly. Plus, the installer is way faster. PNPM just creates a link instead of downloading anything fresh. And the disk savings? Exactly. 50 copies drops down to one.

[00:01:31]>> Is NPM even worth keeping? For a tiny project on your laptop, NPM is completely fine. It ships with Node with no setup. The real wins start to show up the moment you have a monorepo, a shared CI, or a laptop with a lot of projects on it.

[00:01:42]>> Damn, this is not bad. Intern, where are you learning this stuff?

[00:01:44]>> It's actually super simple. I'd recommend going to learn.next.org, and you can generate a free project that's going to teach you exactly all this. You should definitely do it. All right, I'm going to take care of it.