Add TypeScript definition (#4)

index.d.ts

@@ -0,0 +1,48 @@
+declare namespace pkgUp {
+	interface Options {
+		/**
+		Directory to start from.
+
+		@default process.cwd()
+		*/
+		readonly cwd?: string;
+	}
+}
+
+declare const pkgUp: {
+	/**
+	Find the closest `package.json` file.
+
+	@returns The filepath, or `null` if it couldn't be found.
+
+	@example
+	```
+	// /
+	// └── Users
+	//     └── sindresorhus
+	//         └── foo
+	//             ├── package.json
+	//             └── bar
+	//                 ├── baz
+	//                 └── example.js
+
+	// example.js
+	import pkgUp = require('pkg-up');
+
+	(async () => {
+		console.log(await pkgUp());
+		//=> '/Users/sindresorhus/foo/package.json'
+	})();
+	```
+	*/
+	(options?: pkgUp.Options): Promise<string | null>;
+
+	/**
+	Synchronously find the closest `package.json` file.
+
+	@returns The filepath, or `null` if it couldn't be found.
+	*/
+	sync(options?: pkgUp.Options): string | null;
+};
+
+export = pkgUp;

index.test-d.ts

@@ -0,0 +1,7 @@
+import {expectType} from 'tsd';
+import pkgUp = require('.');
+
+expectType<Promise<string | null>>(pkgUp());
+expectType<Promise<string | null>>(pkgUp({cwd: '.'}));
+expectType<string | null>(pkgUp.sync());
+expectType<string | null>(pkgUp.sync({cwd: '.'}));

package.json

@@ -13,10 +13,11 @@
 		"node": ">=8"
 	},
 	"scripts": {
-		"test": "xo && ava"
+		"test": "xo && ava && tsd"
 	},
 	"files": [
-		"index.js"
+		"index.js",
+		"index.d.ts"
 	],
 	"keywords": [
 		"pkg",
@@ -44,7 +45,8 @@
 		"find-up": "^3.0.0"
 	},
 	"devDependencies": {
-		"ava": "^1.3.1",
+		"ava": "^1.4.1",
+		"tsd": "^0.7.2",
 		"xo": "^0.24.0"
 	}
 }