github action: automate version bump on merge to main



~3 min read


529 words

I spent a few hours this weekend writing a Github action to accomplish a different way of managing the versions of my library.

I think the final answer is actually quite readable, which makes me quite happy!

First, the Github workflow, saved in .github/workflows/bumpVersionOnPushToMain.yml:

name: "Update the package version on pushes to main"
      - main
    runs-on: ubuntu-latest
      - uses: actions/checkout@v2
      - run: chmod +x ./scripts/incrementMinor.js
      - run: ./scripts/incrementMinor.js
      - uses: stefanzweifel/git-auto-commit-action@v4
          commit_message: "Automated version bump on merge to main"

One of the things I stumbled over as this was one of the first Github Action I’d written was how I could access the actual code. It turns out that’s exactly what actions/checkout@v2 is for - and by default it checks out the current repository.

Before I was using that action, the following lines which assume the presence of files failed.

Now, let’s step through the actual pieces.

The script of incrementMinor is just a few lines of code. In time I’d love to make this “smarter” so that it can receive arguments to dictate which version to increment.

#!/usr/bin/env node
const { incrementVersion } = require("./incrementVersion")

function incMinorVersion(version) {
  const [major, minor, patch] = version.split(".")
  if (isNaN(Number(minor)))
    throw Error(`Version is not made up of numbers! "${version}"`)
  const newMinor = String(Number(minor) + 1)
  return [major, newMinor, patch].join(".")


The way this works is that this function is actually passed into a more generic incrementVersion function which receives an incrementer:

const fs = require("fs")
const { getLatestVersion } = require("./getVersion")
const { saveVersion } = require("./saveVersion")

function incrementVersion(incrementer) {
  // read and parse package.json
  const rawPackage = fs.readFileSync("./package.json")
  const parsedPackage = JSON.parse(rawPackage)

  // get latest published version
  const latestVersion = getLatestVersion(parsedPackage)

  // update the version
  const nextVersion = incrementer(latestVersion)
  parsedPackage.version = nextVersion

  // save and commit the package.json

module.exports = { incrementVersion }

This has two helper functions of its own:

  1. getLatestVersion and
  2. saveVersion

First the getLatestVersion:

const { spawnSync } = require("child_process")

function getLatestVersion(packageJson) {
  let latestVersion
  const latestPublishedVersion = spawnSync("npm", [

  if (latestPublishedVersion.stderr.toString()) {
    // The package has never been published
    latestVersion = packageJson.version
  } else {
    latestVersion = latestPublishedVersion.stdout.toString().trim()

  return latestVersion

module.exports = { getLatestVersion }
const fs = require("fs")
const { gitAdd, gitCommit } = require("./simpleGit")

function saveVersion(packageJson) {
  const { version } = packageJson

    Buffer.from(JSON.stringify(packageJson, null, 2)),
    { encoding: "utf8" },
    (err) => {
      if (err) {
        return console.log("Error!", err)

      gitCommit(`Published version: ${version}`)

      return console.log(
        `Successfully updated and committed package.json to version ${version}`,

module.exports = { saveVersion }

This one uses a few “simple” git commands:

const { spawnSync } = require("child_process")

const gitAdd = () => spawnSync("git", ["add", "package.json"])
const gitCommit = (message) => spawnSync("git", ["commit", `-m '${message}'`])

module.exports = { gitAdd, gitCommit }

All of these helper scripts rely on the spawnSync method on the child_process module.

That’s the whole thing. With this workflow in place, whenever code is merged to main, I run a workflow that will automatically bump the minor version of the project.

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