Add TypeScript definition

index.d.ts

@@ -0,0 +1,23 @@
+export interface ShellEnv {
+    readonly [x: string]: string;
+    readonly SHELL: string;
+    readonly TERM_PROGRAM: string;
+}
+
+/**
+ * Get the environment variables defined in your dotfiles.
+ *
+ * @param shell To read the environment variables from.
+ * @returns The environment variables.
+ */
+export function sync(shell?: string): ShellEnv;
+
+/**
+ * Get the environment variables defined in your dotfiles.
+ * 
+ * @param shell To read the environment variables from.
+ * @returns The environment variables.
+ */
+export function shellEnv(shell?: string): Promise<ShellEnv>;
+
+export default shellEnv;

index.test-d.ts

@@ -0,0 +1,7 @@
+import {expectType} from 'tsd-check';
+import shellEnv, { sync, ShellEnv } from '.';
+
+(async () => {
+    expectType<ShellEnv>(sync());
+    expectType<ShellEnv>(await shellEnv());
+})();

package.json

@@ -13,10 +13,11 @@
 		"node": ">=6"
 	},
 	"scripts": {
-		"test": "xo && ava"
+		"test": "xo && ava && tsd-check"
 	},
 	"files": [
-		"index.js"
+		"index.js",
+		"index.d.ts"
 	],
 	"keywords": [
 		"env",
@@ -39,6 +40,12 @@
 	},
 	"devDependencies": {
 		"ava": "*",
+		"tsd-check": "^0.2.1",
 		"xo": "*"
+	},
+	"xo": {
+		"ignores": [
+			"*.ts"
+		]
 	}
 }