diff --git a/index.js b/index.ts
similarity index 93%
rename from index.js
rename to index.ts
index 7f7736d..5269bd0 100644
--- a/index.js
+++ b/index.ts
@@ -5,9 +5,7 @@
  * Released under the MIT License.
  */
 
-'use strict';
-
-module.exports = function(arr) {
+export = function(arr: Array<string | number>) {
   if (!Array.isArray(arr)) {
     throw new TypeError('expected an array');
   }
diff --git a/package.json b/package.json
index 5c8b8d4..d2fbf41 100644
--- a/package.json
+++ b/package.json
@@ -19,15 +19,19 @@
     "index.js"
   ],
   "main": "index.js",
+  "types": "index.d.ts",
   "engines": {
     "node": ">=0.10.0"
   },
   "scripts": {
+    "build": "tsc --declaration index.ts",
+    "pretest": "tsc index.ts",
     "test": "mocha"
   },
   "devDependencies": {
     "gulp-format-md": "^0.1.12",
-    "mocha": "^3.3.0"
+    "mocha": "^3.3.0",
+    "typescript": "^2.8.1"
   },
   "keywords": [
     "array",