Add TypeScript definition (#11)

Co-authored-by: Sindre Sorhus <sindresorhus@gmail.com>

index.d.ts

@@ -0,0 +1,22 @@
+/**
+Returns `true` if the given `moduleName` is a Node.js builtin module, `false` otherwise.
+
+@param moduleName  - The name of the module.
+
+@example
+```
+import isBuiltinModule = require('is-builtin-module');
+
+isBuiltinModule('fs/promises');
+//=> true
+
+isBuiltinModule('node:fs');
+//=> true
+
+isBuiltinModule('unicorn');
+//=> false
+```
+*/
+declare function isBuiltinModule(moduleName: string): boolean;
+
+export = isBuiltinModule;

index.test-d.ts

@@ -0,0 +1,5 @@
+import {expectType, expectError} from 'tsd';
+import isBuiltinModule = require('.');
+
+expectType<(moduleName: string) => boolean>(isBuiltinModule);
+expectError<() => boolean>(isBuiltinModule);

package.json

@@ -7,16 +7,17 @@
 	"author": {
 		"name": "Sindre Sorhus",
 		"email": "sindresorhus@gmail.com",
-		"url": "sindresorhus.com"
+		"url": "https://sindresorhus.com"
 	},
 	"engines": {
 		"node": ">=6"
 	},
 	"scripts": {
-		"test": "xo && ava"
+		"test": "xo && ava && tsd"
 	},
 	"files": [
-		"index.js"
+		"index.js",
+		"index.d.ts"
 	],
 	"keywords": [
 		"builtin",
@@ -39,6 +40,7 @@
 	},
 	"devDependencies": {
 		"ava": "^0.25.0",
+		"tsd": "^0.7.2",
 		"xo": "^0.23.0"
 	}
 }