add github actions for PR checks

.github/workflows/nodejs.yaml

@@ -0,0 +1,25 @@
+name: CI
+
+on: [push]
+
+jobs:
+  build:
+
+    runs-on: ubuntu-latest
+
+    strategy:
+      matrix:
+        node-version: [12.x]
+
+    steps:
+    - uses: actions/checkout@v1
+    - name: Use Node.js ${{ matrix.node-version }}
+      uses: actions/setup-node@v1
+      with:
+        node-version: ${{ matrix.node-version }}
+    - name: install dependencies
+      run: npm ci && npm run install-peers
+    - name: check types
+      run: npm run types
+    - name: unit tests
+      run: npm test

package.json

@@ -8,6 +8,7 @@
     "preversion": "npm run clean && npm ci && npm run types",
     "postversion": "npm run prep && npm publish dist && git push --follow-tags",
     "prep": "rm -rf dist && copyfiles ./src/* package.json README.md -f -a ./dist/",
+    "install-peers": "npm i immer@8 --no-save",
     "clean": "rm -rf node_modules",
     "types": "tsc",
     "test": "jest"