add publish action file

.github/workflows/publish.yml

@@ -0,0 +1,45 @@
+name: Publish npm package
+
+on:
+  push:
+    branches:
+      - main
+
+jobs:
+  publish:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v2
+
+      - name: Setup Node.js
+        uses: actions/setup-node@v2
+        with:
+          node-version: '14'
+          registry-url: 'https://registry.npmjs.org'
+
+      - name: Install dependencies
+        run: pnpm i
+
+      - name: Run tests
+        run: pnpm test
+
+      - name: Check if version changed
+        id: version_check
+        run: |
+          git fetch origin main
+          PREVIOUS_VERSION=$(git show origin/main:package.json | jq -r .version)
+          CURRENT_VERSION=$(jq -r .version package.json)
+          echo "previous_version=$PREVIOUS_VERSION" >> $GITHUB_OUTPUT
+          echo "current_version=$CURRENT_VERSION" >> $GITHUB_OUTPUT
+          if [ "$PREVIOUS_VERSION" == "$CURRENT_VERSION" ]; then
+            echo "Version has not changed. Exiting."
+            exit 0
+          fi
+
+      - name: Publish to npm
+        if: ${{ steps.version_check.outputs.current_version != steps.version_check.outputs.previous_version }}
+        run: pnpm publish
+        env:
+          NODE_AUTH_TOKEN: ${{ secrets.NPM_TOKEN }}