[New] add types

index.d.ts

@@ -0,0 +1,3 @@
+declare function isGeneratorFunction(fn: unknown): fn is GeneratorFunction;
+
+export = isGeneratorFunction;

index.js

@@ -18,8 +18,10 @@ var getGeneratorFunc = function () { // eslint-disable-line consistent-return
 	} catch (e) {
 	}
 };
+/** @type {undefined | false | null | GeneratorFunctionConstructor} */
 var GeneratorFunction;
 
+/** @type {import('.')} */
 module.exports = function isGeneratorFunction(fn) {
 	if (typeof fn !== 'function') {
 		return false;
@@ -36,7 +38,10 @@ module.exports = function isGeneratorFunction(fn) {
 	}
 	if (typeof GeneratorFunction === 'undefined') {
 		var generatorFunc = getGeneratorFunc();
-		GeneratorFunction = generatorFunc ? getProto(generatorFunc) : false;
+		GeneratorFunction = generatorFunc
+			// eslint-disable-next-line no-extra-parens
+			? /** @type {GeneratorFunctionConstructor} */ (getProto(generatorFunc))
+			: false;
 	}
 	return getProto(fn) === GeneratorFunction;
 };

package.json

@@ -17,6 +17,7 @@
 		"test:uglified": "node test/uglified",
 		"posttest": "npx npm@\">= 10.2\" audit --production",
 		"lint": "eslint --ext=js,mjs .",
+		"postlint": "tsc && attw -P",
 		"version": "auto-changelog && git add CHANGELOG.md",
 		"postversion": "auto-changelog && git add CHANGELOG.md && git commit --no-edit --amend && git tag -f \"v$(node -e \"console.log(require('./package.json').version)\")\""
 	},
@@ -48,7 +49,12 @@
 		"safe-regex-test": "^1.1.0"
 	},
 	"devDependencies": {
+		"@arethetypeswrong/cli": "^0.17.2",
 		"@ljharb/eslint-config": "^21.1.1",
+		"@ljharb/tsconfig": "^0.2.3",
+		"@types/for-each": "^0.3.3",
+		"@types/make-generator-function": "^2.0.3",
+		"@types/tape": "^5.8.0",
 		"auto-changelog": "^2.5.0",
 		"core-js": "^2.6.5 || ^3.20.0",
 		"encoding": "^0.1.13",
@@ -60,6 +66,7 @@
 		"nyc": "^10.3.2",
 		"safe-publish-latest": "^2.0.0",
 		"tape": "^5.9.0",
+		"typescript": "next",
 		"uglify-register": "^1.0.1"
 	},
 	"testling": {

test/corejs.js

@@ -1,5 +1,6 @@
 'use strict';
 
+// @ts-ignore
 require('core-js');
 
 require('./');

test/index.js

@@ -58,6 +58,7 @@ test('returns false for non-generator function with faked toString', function (t
 
 test('returns false for non-generator function with faked @@toStringTag', { skip: !hasToStringTag || generatorFuncs.length === 0 }, function (t) {
 	var generatorFunc = generatorFuncs[0];
+	/** @type {{ toString(): unknown; valueOf(): unknown; [Symbol.toStringTag]?: unknown; }} */
 	var fakeGenFunction = {
 		toString: function () { return String(generatorFunc); },
 		valueOf: function () { return generatorFunc; }

test/uglified.js

@@ -1,5 +1,6 @@
 'use strict';
 
+// @ts-ignore
 require('uglify-register/api').register({
 	exclude: [/\/node_modules\//, /\/test\//],
 	uglify: { mangle: true }

tsconfig.json

@@ -0,0 +1,9 @@
+{
+  "extends": "@ljharb/tsconfig",
+  "compilerOptions": {
+    "maxNodeModuleJsDepth": 0
+  },
+  "exclude": [
+    "coverage"
+  ]
+}