Easy Automatic npm Publishes

One common question from people using npm to publish, especially on CI systems, is how best to automate the process, especially when dealing with multiple branches.

For a while now, I've been using a pattern that takes almost all of the human interaction out of it, since I tend to mess stuff up when I type it with my fingers. This works well for automatic publishes from CI or when publishing manually from a terminal.

I haven't manually typed npm publish in a while, which is a good thing.

First things first, have good tests

I am a huge fan of running tests with 100% test coverage. It isn't a perfect guard against every problem out there, but it does keep me from doing stupid things, like assuming that I know what my program does.

My go-to test library is tap, but you can do this with any testing library that supports code coverage. If it doesn't support code coverage out of the box, you can use nyc to run any Node.js process with coverage tracking.

To use it, run npm i tap -D, and then add this to your scripts section in package.json:

{
  "scripts": {
    "test": "tap"
  },
  "tap": {
    "check-coverage": true
  }
}

The npm version Command

The npm version command will figure out what the next version should be, edit your package.json file, and even check it into git with a signed tag. The beauty of this is that it also prevents you from bumping the version when you have untracked changes in your git working directory, and provides some hook scripts that can do other things before or after the version bump.

In the scripts section of my package.json file, I add a preversion script that runs my tests:

{
  "scripts": {
    "preversion": "npm test",
    "test": "tap"
  },
  "tap": {
    "check-coverage": true
  }
}

Now, before I can bump the version, npm will make sure that my tests pass. If the test fails (or if coverage isn't 100%), then it'll fail and the version command fails.

Publishing on Version Change

Bumping the version is fine, but then it's time to share it. Along with preversion, the postversion command does actions after the version is bumped. So, let's hook onto that to publish the package.

{
  "scripts": {
    "postversion": "npm publish",
    "preversion": "npm test",
    "test": "tap"
  },
  "tap": {
    "check-coverage": true
  }
}

Keeping Git and npm in Sync

That's fine for pushing to npm, but then I have to remember to push the changes to git. (I have many times forgotten to do this, and gotten issues because the code on npm is not in GitHub, which is generally a bad sign.)

Thankfully, npm also gives us a way to hook a script around the publish event, so let's use that:

{
  "scripts": {
    "postpublish": "git push origin --all; git push origin --tags",
    "postversion": "npm publish",
    "preversion": "npm test",
    "test": "tap"
  },
  "tap": {
    "check-coverage": true
  }
}

This runs two commands. The first pushes all branches, and the second pushes all the tags (including my newly published version tag).

Branches and Dist-Tags

Occasionally, I'll find myself working on some big feature for a new release that is not yet ready for prime time.

In the feature branch, I'll modify the scripts by adding a --tag argument to the npm publish command to put it on a dist-tag other than latest.

{
  "scripts": {
    "postversion": "npm publish --tag=next",
    "postpublish": "git push origin --all; git push origin --tags",
    "preversion": "npm test",
    "test": "tap"
  },
  "tap": {
    "check-coverage": true
  }
}

Now, I can tell people to run npm install my-module@next to try out the new prerelease version.

On the other side, I might want to land a bugfix or backport a feature for a legacy version. To do that, I create a git branch with the old version, and update package.json to add a legacy tag instead.

{
  "scripts": {
    "postversion": "npm publish --tag=legacy",
    "postpublish": "git push origin --all; git push origin --tags",
    "preversion": "npm test",
    "test": "tap"
  },
  "tap": {
    "check-coverage": true
  }
}

Bonus Points: Sign Your Versions

Git has support for PGP signing tagged commits. To tell npm to take advantage of this, set these two config values:

npm config set sign-git-commit true
npm config set sign-git-tag true

If setting up PGP and hooking it up with Git is too much of a pain, you're not alone. I'm a nerd who's been computering for a very long time, and I can't handle it. Also, I'm always worried about my keys just sitting on my machine in text files, even if they are encrypted with a passphrase. And if they are encrypted with a passphrase, then I have to type it in all the time, and that's just too much work.

I'm a huge fan of Krypton. It stores your PGP and SSH private keys in your mobile device's secure storage vault, and then sends a push notification to allow it to do things with those keys. It's dead-simple to set up, and extremely easy to use, and gives you a hardware second factor for everything that matters.

Of course, and I don't exactly know if this is a bug or a feature, it does mean that whenever I run npm version, between the commit, the signature, the tag, and the two SSH connections, my phone does a lot of buzzing.

Running npm version to Test and Publish

From there, I use the npm version command to do all my publishing. For bug fixes, I run npm version patch. For new features, I run npm version minor. For breaking changes, I run npm version major.

If you use Conventional Commits or similar tools, you could even automate the detection of what kind of version bump it should be, though that's left as an exercise for the reader.

This approach of using npm scripts to automate the process works well with any system where you'll be publishing and committing. Set it up in your next project, and trust your human fingers a little bit less :)

PS: npm Configuration is Very Flexible

You'll note that I did --tag=<whatever> in the publish commands above. You can also configure npm in many other ways. Any configuration value (including tag in the case of npm publish) can be set:

  • explicitly on the command line, like --tag=whatever
  • in the environment, like NPM_CONFIG_TAG=whatever
  • in a .npmrc file in the root of your project, like tag = whatever
  • in a .npmrc file in your home directory
  • in /usr/local/etc/npmrc (or /usr/etc/npmrc on some systems).

This works inheritance-style, so the higher up on that list a setting is, the higher the priority.

For CI/CD systems, this means that you can sometimes set environment variables to control the behavior of npm commands, without having to change the code or inject files into places. If it's easier to control it with a file (for example, checking a .npmrc file into git), then that's also fine.