eslint: config

.eslintrc

@@ -0,0 +1,20 @@
+{
+  "parserOptions": {
+    "ecmaVersion": 2019,
+    "sourceType": "module",
+    "ecmaFeatures": {
+      "jsx": true
+    }
+  },
+  "rules": {
+    "strict": ["error", "never"],
+    "valid-typeof": "error",
+    "no-unsafe-negation": "error",
+    "no-unused-vars": "error",
+    "no-unexpected-multiline": "error",
+    "no-undef": "error"
+  },
+  "env": {
+    "browser": true
+  }
+}

package.json

@@ -9,6 +9,7 @@
   "devDependencies": {
     "@babel/cli": "^7.5.5",
     "@babel/core": "^7.5.5",
-    "@babel/preset-env": "^7.5.5"
+    "@babel/preset-env": "^7.5.5",
+    "eslint": "^6.1.0"
   }
 }