Add TypeScript definition

Closes #11

Author: Glazy

index.d.ts

@@ -0,0 +1,35 @@
+import { Container } from "unstated";
+
+declare const UNSTATED: {
+	/**
+	An object containing the project's containers.
+	*/
+	containers: {
+		[containerName: string]: Container<{ [stateName: string]: unknown }>;
+	};
+
+	/**
+	Whether the debugger should be enabled or not.
+	*/
+	isEnabled: boolean;
+
+	/**
+	Function that logs out the current state.
+	*/
+	logState: () => void;
+
+	/**
+	Boolean value that represents whether state changes should be logged to the
+	console.
+	*/
+	logStateChanges: boolean;
+
+	/**
+	An object containing all of the state values.
+	*/
+	states: {
+		[containerName: string]: { [stateName: string]: unknown };
+	};
+};
+
+export default UNSTATED;

index.test-d.ts

@@ -0,0 +1,17 @@
+import { expectType } from "tsd-check";
+import UNSTATED from "./index";
+import { Container } from "unstated";
+
+expectType<boolean>(UNSTATED.isEnabled);
+expectType<boolean>(UNSTATED.logStateChanges);
+
+expectType<{
+	[containerName: string]: Container<{ [stateName: string]: unknown }>;
+}>(UNSTATED.containers);
+
+expectType<() => void>(UNSTATED.logState);
+expectType<void>(UNSTATED.logState());
+
+expectType<{ [containerName: string]: { [stateName: string]: unknown } }>(
+	UNSTATED.states
+);

package.json

@@ -13,10 +13,11 @@
 		"node": ">=8"
 	},
 	"scripts": {
-		"test": "xo && ava"
+		"test": "xo && ava && tsd-check"
 	},
 	"files": [
-		"index.js"
+		"index.js",
+		"index.d.ts"
 	],
 	"keywords": [
 		"unstated",
@@ -38,6 +39,7 @@
 		"ava": "*",
 		"browser-env": "^3.2.5",
 		"react": "^16.3.0",
+		"tsd-check": "^0.6.0",
 		"unstated": "^2.0.2",
 		"xo": "*"
 	},
@@ -48,6 +50,9 @@
 		"envs": [
 			"node",
 			"browser"
+		],
+		"ignores": [
+			"*.ts"
 		]
 	},
 	"ava": {