Add CI/CD step to check cdn files are up to date (#148)

* check cdn files match the source

* base64 encode checksum result

* trim new lines on checksum output

.github/workflows/test-on-pr.yml

@@ -25,3 +25,34 @@ jobs:
           node-version: '16.x'
       - run: yarn
       - run: yarn format:check
+  verify-cdn-build-matches-src:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - uses: actions/setup-node@v3
+        with:
+          node-version: '16.x'
+      - run: yarn
+      - run: npm install -g checksum
+      - name: Calc current cdn checksums
+        id: current-checksums
+        run: echo "checksums=$(checksum cdn/* | base64 | tr '\n' ' ')" >> $GITHUB_OUTPUT
+      - run: yarn build
+      - name: Calc built cdn checksums
+        id: built-checksums
+        run: echo "checksums=$(checksum cdn/* | base64 | tr '\n' ' ')" >> $GITHUB_OUTPUT
+      - uses: actions/github-script@v6
+        env:
+          CURRENT_CHECKSUMS: ${{steps.current-checksums.outputs.checksums}}
+          BUILT_CHECKSUMS: ${{steps.built-checksums.outputs.checksums}}
+        with:
+          script: |
+            const { 
+              CURRENT_CHECKSUMS: current, 
+              BUILT_CHECKSUMS: built 
+            } = process.env
+            if (current.trim() !== built.trim()) {
+              core.setFailed(`The files in the cdn directory don't match the expected output given the source. Maybe you didn't run yarn build before pushing?`)
+            } else {
+              core.debug(`Success, the cdn build files reflect the current source code.`)
+            }