What is the difference between npm-shrinkwrap.json and package-lock.json?

With the release of npm@5, it will now write a package-lock.json unless a npm-shrinkwrap.json already exists.

I installed npm@5 globally via:

npm install npm@5 -g

And now, if a npm-shrinkwrap.json is found during:

npm install

a warning will be printed:

npm WARN read-shrinkwrap This version of npm
is compatible with lockfileVersion@1,
but npm-shrinkwrap.json was generated for lockfileVersion@0.
I'll try to do my best with it!

So my take-away is that I should replace the shrinkwrap with the package-lock.json.

Yet why is there a new format for it? What can the package-lock.json do that the npm-shrinkwrap.json cannot?

The files have exactly the same content, but there are a handful of differences in how npm handles them, most of which are noted on the docs pages for package-lock.json and npm-shrinkwrap.json:

• package-lock.json is never published to npm, whereas npm-shrinkwrap is by default
• package-lock.json files that are not in the top-level package are ignored, but shrinkwrap files belonging to dependencies are respected
• npm-shrinkwrap.json is backwards-compatible with npm versions 2, 3, and 4, whereas package-lock.json is only recognized by npm 5+

You can convert an existing package-lock.json to an npm-shrinkwrap.json by running npm shrinkwrap.

Thus:

• If you are not publishing your package to npm, the choice between these two files is of little consequence. You may wish to use package-lock.json because it is the default and its name is clearer to npm beginners; alternatively, you may wish to use npm-shrinkwrap.json for backwards compatibility with npm 2-4 if it is difficult for you to ensure everyone on your development team is on npm 5+. (Note that npm 5 was released on 25th May 2017; backwards compatibility will become less and less important the further we get from that date, as most people will eventually upgrade.)

• If you are publishing your package to npm, you have a choice between:

  1. using a package-lock.json to record exactly which versions of dependencies you installed, but allowing people installing your package to use any version of the dependencies that is compatible with the version ranges dictated by your package.json, or
  2. using an npm-shrinkwrap.json to guarantee that everyone who installs your package gets exactly the same version of all dependencies

  
  The official view described in the docs is that option 1 should be used for libraries (presumably in order to reduce the amount of package duplication caused when lots of a package's dependencies all depend on slightly different versions of the same secondary dependency), but that option 2 might be reasonable for executables that are going to be installed globally.

Explanation from NPM Developer:

> The idea is definitely for package-lock.json to be the Latest and > Greatest in shrinkwrap technology, and npm-shrinkwrap.json to be > reserved for those precious few folks out there who care very much > about their libraries having an exact node_modules -- and for people > who want CI using npm@>=2 to install a particular tree without having > to bump its npm version. > > The new lockfile ("package-lock.json") shares basically all of the > same code, the exact same format as npm-shrinkwrap (you can rename > them between one another!). It's also something the community seems to > understand: "it has a lockfile" seems to click so much faster with > people. Finally, having a new file meant that we could have relatively > low-risk backwards-compat with shrinkwrap without having to do weird > things like allow-publication mentioned in the parent post.

I think the idea was to have --save and shrinkwrap happen by default but avoid any potential issues with a shrinkwrap happening where it wasn't wanted. So, they just gave it a new file name to avoid any conflicts. Someone from npm explained it more thoroughly here:

https://www.reddit.com/r/javascript/comments/6dgnnq/npm_v500_released_save_by_default_lockfile_better/di3mjuk/

The relevant quote:

> npm publishes most files in your source directory by default, and > people have been publishing shrinkwraps for years. We didn't want to > break compatibility. With --save and shrinkwrap by default, there was > a great risk of it accidentally making it in and propagating through > the registry, and basically render our ability to update deps and > dedupe... null. > > So we chose a new name. And we chose a new name kind of all of a > sudden. The new lockfile shares basically all of the same code, the > exact same format

package-lock.json versions are guaranteed with only npm ci (since npm install overwrites package-lock.json if there is a conflict with package.json).

npm-shrinkwrap.json versions are guaranteed with both npm ci and npm install.