Node Package Manager 4 --- Changes to Prepublish (NPM)

November 10, 2016
Lucas Holmquist

NPM 4 was released recently, about 2 weeks ago, and with it came some major changes. Some breaking, some not, but there is an interesting deprecation that happened with regards to the prepublish script.

Currently, if you had a prepublish entry in your package.json:

{
  scripts: {
    prepublish: "nsp check"
  }
}

This would be run whenever you performed a npm publish. Which is probably what you would expect with a name like prepublish.

Another thing was also happening though. When you ran npm install with no arguments, the prepublish step would still be run --- this is not what you would expect.

Example:

$ ~/publish-change » npm install

> publish-change@0.0.1 prepublish
> nsp check

(+) No known vulnerabilities found

So a few things are happening in NPM 4.

First, there is now a new life-cycle script called prepare, which runs during npm install.

{
  scripts: {
    prepare: "nsp check"
  }
}

Using our previous example:

$ ~/publish-change » npm4 install

> publish-change@0.0.1 prepare
> nsp check

(+) No known vulnerabilities found

note: there is no npm4 command, I'm just using that to illustrate me running different versions

Second, there is now a temporary prepublishOnly life-cycle script. This will only run during a npm publish

Third, prepublish has been deprecated, but not the whole thing. I know, this is the interesting part. The part of prepublish that ran during the those no argument npm installs is the part that is deprecated, that part is now actually npm prepare.

This is the warning message produced when running npm prepublish in NPM 4:

npm WARN prepublish-on-install As of npm@5, `prepublish` scripts will run only for `npm publish`.

npm WARN prepublish-on-install (In npm@4 and previous versions, it also runs for `npm install`.)

npm WARN prepublish-on-install See the deprecation note in `npm help scripts` for more information.

So if you are relying on your prepublish scripts to do anything for you during a npm install, you might want to update to using the prepare and prepublishOnly scripts for the time being.

At some point in the future, prepublishOnly will be removed and you can go back to using just prepublish and prepare(if needed).