One of the biggest problems right now with Node is how fast it is changing. This means that production systems can be very fragile and an npm update can easily break things.

Using bundledDependencies is a way to get round this issue by ensuring, as you correctly surmise, that you will always deliver the correct dependencies no matter what else may be changing.

You can also use this to bundle up your own, private bundles and deliver them with the install.

Other advantage is that you can put your internal dependencies (application components) there and then just require them in your app as if they were independent modules instead of cluttering your lib/ and publishing them to npm.

If/when they are matured to the point they could live as separate modules, you can put them on npm easily, without modifying your code.

For the quick reader : this QA is about the package.json bundledDependencies field, not about the package.

What bundledDependencies do

"bundledDependencies" are exactly what their name implies. Dependencies that should be inside your project. So the functionality is basically the same as normal dependencies. They will also be packed when running npm pack.

When to use them

Normal dependencies are usually installed from the npm registry. Thus bundled dependencies are useful when:

• you want to re-use a third party library that doesn't come from the npm registry or that was modified
• you want to re-use your own projects as modules
• you want to distribute some files with your module

This way, you don't have to create (and maintain) your own npm repository, but get the same benefits that you get from npm packages.

When not to use bundled dependencies

When developing, I don't think that the main point is to prevent accidental updates though. We have better tools for that, namely code repositories (git, mercurial, svn...) or now lock files.

To pin your package versions, you can use:

• Option1: Use the newer NPM version 5 that comes with node 8. It uses a package-lock.json file (see the node blog and the node 8 release)

• Option2: use yarn instead of npm. It is a package manager from facebook, faster than npm and it uses a yarn.lock file. It uses the same package.json otherwise.

This is comparable to lockfiles in other package managers like Bundler or Cargo. It’s similar to npm’s npm-shrinkwrap.json, however it’s not lossy and it creates reproducible results.

npm actually copied that feature from yarn, amongst other things.

• Option3: this was the previously recommended approach, which I do not recommend anymore. The idea was to use npm shrinkwrap most of the time, and sometimes put the whole thing, including the node_module folder, into your code repository. Or possibly use shrinkpack. The best practices at the time were discussed on the node.js blog and on the joyent developer websites.

See also

This is a bit outside the scope of the question, but I'd like to mention the last kind of dependencies (that I know of): peer dependencies. Also see this related SO question and possibly the docs of yarn on bundledDependencies.

Operationally, I look at bundledDependencies as a module's private module store, where dependencies is more public, resolved among your module and its dependencies (and sub-dependencies). Your module may rely on an older version of, say, react, but a dependency requires latest-and-greatest. Your package/install will result in your pinned version in node_modules/$yourmodule/node_modules/react, while your dependency will get their version in node_modules/react (or node_modules/$dependency/node_modules/react if they're so inclined).

A caveat: I recently ran into a dependency that did not properly configure its dependency on react, and having react in bundledDependencies caused that dependent module to fail at runtime.

I'm surprised I didn't see this here already, but when carefully selected, bundledDependencies can be used to produce a distributable package from npm pack that will run on a system where npm is not configured. This is helpful if you have e.g. a system that's not networked / not on the internet: bring your package over on a thumb drive (or whatever) and unpack the tarball, then npm run or node index.js and it Just Works.

Maybe there's a better way to bundle up your application to run "offline", but if there is I haven't found it.