Add eslint.

.eslintrc.json

@@ -0,0 +1,32 @@
+{
+  "env": {
+    "browser": true,
+    "node": true
+  },
+  "extends": [
+    "eslint:recommended",
+    "plugin:react/recommended"
+  ],
+  "parserOptions": {
+    "ecmaVersion": "latest",
+    "sourceType": "module"
+  },
+  "plugins": [
+    "react"
+  ],
+  "rules": {
+    "react/prop-types": "off"
+  },
+  "overrides": [
+    {
+      "files": [
+        "src/**/*.jsx"
+      ]
+    }
+  ],
+  "settings": {
+    "react": {
+      "version": "detect"
+    }
+  }
+}

.github/workflows/linux.yml

@@ -24,5 +24,6 @@ jobs:
         node-version: ${{ matrix.node-version }}
         cache: 'npm'
     - run: npm ci
-    - run: npm run build --if-present
-    - run: npm run test --if-present
+    - run: npx eslint ./src/
+    - run: npm run build
+    - run: npm run test