Add ESLint (#941)

* Add eslint, switch to lint-staged for precommit

* Fix all ESLint errors

* Update GH workflow to check prettier and eslint

.github/workflows/build.yml

@@ -24,5 +24,7 @@ jobs:
         node-version: ${{ matrix.node-version }}
         cache: 'npm'
     - run: npm ci
+    - run: npx eslint .
+    - run: npx prettier --check .
     - run: npm run build --if-present
     - run: npm run test --if-present