add lint-staged

.babelrc

@@ -7,6 +7,7 @@
           "node": "10"
         }
       }
-    ]
+    ],
+    "@babel/preset-typescript"
   ]
-}
+}

.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"
+      ]
+    }
+  ]
 }

.huskyrc

@@ -0,0 +1,5 @@
+{
+  "hooks": {
+    "pre-commit": "npm run check-types && lint-staged"
+  }
+}

.lintstagedrc

@@ -0,0 +1,9 @@
+{
+  "*.+(js|ts|tsx)": [
+    "eslint"
+  ],
+  "*.+(js|json|ts|tsx)": [
+    "prettier --write",
+    "git add"
+  ]
+}

package.json

@@ -4,19 +4,26 @@
   "author": "Kent C. Dodds (http://kentcdodds.com/)",
   "license": "GPLv3",
   "scripts": {
-    "build": "babel src --out-dir dist",
-    "lint": "eslint --ignore-path .gitignore .",
-    "prettier": "prettier --ignore-path .gitignore \"**/*.+(js|json)\"",
+    "build": "babel src --extensions .js,.ts,.tsx --out-dir dist",
+    "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",
     "check-format": "npm run prettier -- --list-different",
-    "validate": "npm run check-format && npm run lint && npm run build"
+    "validate": "npm run check-types && npm run check-format && npm run lint && npm run build"
   },
   "devDependencies": {
     "@babel/cli": "^7.7.0",
     "@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"
+    "husky": "^3.0.9",
+    "lint-staged": "^9.4.2",
+    "prettier": "^1.19.1",
+    "typescript": "^3.7.2"
   }
 }

src/typescript-example.js

@@ -1,14 +0,0 @@
-function add(a, b) {
-  return a + b
-}
-
-function getFullName(user) {
-  const {
-    name: {first, middle, last},
-  } = user
-  return [first, middle, last].filter(Boolean).join('')
-}
-
-add(1, 'two')
-
-getFullName({name: {first: 'Joe', midd1e: 'Bud', last: 'Matthews'}})

src/typescript-example.ts

@@ -0,0 +1,21 @@
+function add(a: number, b: number): number {
+  return a + b
+}
+
+interface User {
+  name: {
+    first: string
+    middle: string
+    last: string
+  }
+}
+function getFullName(user: User): string {
+  const {
+    name: {first, middle, last},
+  } = user
+  return [first, middle, last].filter(Boolean).join('')
+}
+
+add(1, 2)
+
+getFullName({name: {first: 'Joe', middle: 'Bud', last: 'Matthews'}})

tsconfig.json

@@ -0,0 +1,6 @@
+{
+  "compilerOptions": {
+    "noEmit": true,
+    "baseUrl": "./src"
+  }
+}