support eslint with typescript

Author: Kent C. Dodds

.eslintrc

@@ -12,5 +12,20 @@
   },
   "env": {
     "browser": true
-  }
+  },
+  "overrides": [
+    {
+      "files": "**/*.+(ts|tsx)",
+      "parser": "@typescript-eslint/parser",
+      "parserOptions": {
+        "project": "./tsconfig.json"
+      },
+      "plugins": ["@typescript-eslint/eslint-plugin"],
+      "extends": [
+        "plugin:@typescript-eslint/eslint-recommended",
+        "plugin:@typescript-eslint/recommended",
+        "eslint-config-prettier/@typescript-eslint"
+      ]
+    }
+  ]
 }

package-lock.json

@@ -5,7 +5,7 @@
   "license": "GPLv3",
   "scripts": {
     "build": "babel src --extensions .js,.ts,.tsx --out-dir dist",
-    "lint": "eslint --ignore-path .gitignore .",
+    "lint": "eslint --ignore-path .gitignore --ext .js,.ts,.tsx .",
     "check-types": "tsc",
     "prettier": "prettier --ignore-path .gitignore \"**/*.+(js|json|ts|tsx)\"",
     "format": "npm run prettier -- --write",
@@ -17,6 +17,8 @@
     "@babel/core": "^7.7.2",
     "@babel/preset-env": "^7.7.1",
     "@babel/preset-typescript": "^7.7.2",
+    "@typescript-eslint/eslint-plugin": "^2.7.0",
+    "@typescript-eslint/parser": "^2.7.0",
     "eslint": "^6.6.0",
     "eslint-config-prettier": "^6.5.0",
     "prettier": "^1.19.1",