[New] add types

.editorconfig

@@ -7,7 +7,7 @@ end_of_line = lf
 charset = utf-8
 trim_trailing_whitespace = true
 insert_final_newline = true
-max_line_length = 150
+max_line_length = 200
 
 [CHANGELOG.md]
 indent_style = space

.eslintrc

@@ -4,6 +4,7 @@
 	"extends": "@ljharb",
 
 	"rules": {
+		"func-style": 0,
 		"id-length": [1],
 	},
 }

index.d.ts

@@ -0,0 +1,3 @@
+declare function isRegex(value: unknown): value is RegExp;
+
+export = isRegex;

index.js

@@ -5,14 +5,19 @@ var hasToStringTag = require('has-tostringtag/shams')();
 var hasOwn = require('hasown');
 var gOPD = require('gopd');
 
+/** @type {import('.')} */
 var fn;
+
 if (hasToStringTag) {
+	/** @type {(receiver: ThisParameterType<typeof RegExp.prototype.exec>, ...args: Parameters<typeof RegExp.prototype.exec>) => ReturnType<typeof RegExp.prototype.exec>} */
 	var $exec = callBound('RegExp.prototype.exec');
+	/** @type {object} */
 	var isRegexMarker = {};
 
 	var throwRegexMarker = function () {
 		throw isRegexMarker;
 	};
+	/** @type {{ toString(): never, valueOf(): never, [Symbol.toPrimitive]?(): never }} */
 	var badStringifier = {
 		toString: throwRegexMarker,
 		valueOf: throwRegexMarker
@@ -22,28 +27,35 @@ if (hasToStringTag) {
 		badStringifier[Symbol.toPrimitive] = throwRegexMarker;
 	}
 
+	/** @type {import('.')} */
+	// @ts-expect-error TS can't figure out that the $exec call always throws
 	// eslint-disable-next-line consistent-return
 	fn = function isRegex(value) {
 		if (!value || typeof value !== 'object') {
 			return false;
 		}
 
-		var descriptor = gOPD(value, 'lastIndex');
+		// eslint-disable-next-line no-extra-parens
+		var descriptor = /** @type {NonNullable<typeof gOPD>} */ (gOPD)(/** @type {{ lastIndex?: unknown }} */ (value), 'lastIndex');
 		var hasLastIndexDataProperty = descriptor && hasOwn(descriptor, 'value');
 		if (!hasLastIndexDataProperty) {
 			return false;
 		}
 
 		try {
-			$exec(value, badStringifier);
+			// eslint-disable-next-line no-extra-parens
+			$exec(value, /** @type {string} */ (/** @type {unknown} */ (badStringifier)));
 		} catch (e) {
 			return e === isRegexMarker;
 		}
 	};
 } else {
+	/** @type {(receiver: ThisParameterType<typeof Object.prototype.toString>, ...args: Parameters<typeof Object.prototype.toString>) => ReturnType<typeof Object.prototype.toString>} */
 	var $toString = callBound('Object.prototype.toString');
+	/** @const @type {'[object RegExp]'} */
 	var regexClass = '[object RegExp]';
 
+	/** @type {import('.')} */
 	fn = function isRegex(value) {
 		// In older browsers, typeof regex incorrectly returns 'function'
 		if (!value || (typeof value !== 'object' && typeof value !== 'function')) {

package.json

@@ -20,6 +20,7 @@
 		"posttest": "npx npm@'>=10.2' audit --production",
 		"prelint": "eclint check $(git ls-files | xargs find 2> /dev/null | grep -vE 'node_modules|\\.git')",
 		"lint": "eslint --ext=js,mjs .",
+		"postlint": "tsc -p . && attw -P",
 		"version": "auto-changelog && git add CHANGELOG.md",
 		"postversion": "auto-changelog && git add CHANGELOG.md && git commit --no-edit --amend && git tag -f \"v$(node -e \"console.log(require('./package.json').version)\")\""
 	},
@@ -46,7 +47,13 @@
 		"hasown": "^2.0.2"
 	},
 	"devDependencies": {
+		"@arethetypeswrong/cli": "^0.17.0",
 		"@ljharb/eslint-config": "^21.1.1",
+		"@ljharb/tsconfig": "^0.2.0",
+		"@types/call-bind": "^1.0.5",
+		"@types/core-js": "^2.5.8",
+		"@types/for-each": "^0.3.3",
+		"@types/tape": "^5.6.5",
 		"auto-changelog": "^2.5.0",
 		"core-js": "^3.39.0",
 		"eclint": "^2.8.1",
@@ -57,7 +64,8 @@
 		"npmignore": "^0.3.1",
 		"nyc": "^10.3.2",
 		"safe-publish-latest": "^2.0.0",
-		"tape": "^5.9.0"
+		"tape": "^5.9.0",
+		"typescript": "^5.8.0-dev.20241129"
 	},
 	"testling": {
 		"files": "test/index.js",

test/index.js

@@ -6,6 +6,7 @@ var test = require('tape');
 var isRegex = require('..');
 
 test('not regexes', function (t) {
+	// @ts-expect-error
 	t.notOk(isRegex(), 'undefined is not regex');
 	t.notOk(isRegex(null), 'null is not regex');
 	t.notOk(isRegex(false), 'false is not regex');
@@ -20,6 +21,7 @@ test('not regexes', function (t) {
 
 test('@@toStringTag', { skip: !hasToStringTag }, function (t) {
 	var regex = /a/g;
+	/** @type {{ toString(): string, valueOf(): RegExp, [Symbol.toStringTag]?: string}} */
 	var fakeRegex = {
 		toString: function () { return String(regex); },
 		valueOf: function () { return regex; }
@@ -39,6 +41,7 @@ test('does not mutate regexes', function (t) {
 	t.test('lastIndex is a marker object', function (st) {
 		var regex = /a/;
 		var marker = {};
+		// @ts-expect-error
 		regex.lastIndex = marker;
 		st.equal(regex.lastIndex, marker, 'lastIndex is the marker object');
 		st.ok(isRegex(regex), 'is regex');
@@ -59,11 +62,14 @@ test('does not mutate regexes', function (t) {
 });
 
 test('does not perform operations observable to Proxies', { skip: typeof Proxy !== 'function' }, function (t) {
-	var Handler = function () {
+	/** @constructor */
+	function Handler() {
+		/** @type (keyof Reflect)[]} */
 		this.trapCalls = [];
-	};
+	}
 
-	forEach([
+	// eslint-disable-next-line no-extra-parens
+	forEach(/** @const @type {(keyof Reflect)[]} */ ([
 		'defineProperty',
 		'deleteProperty',
 		'get',
@@ -75,15 +81,17 @@ test('does not perform operations observable to Proxies', { skip: typeof Proxy !
 		'preventExtensions',
 		'set',
 		'setPrototypeOf'
-	], function (trapName) {
+	]), function (trapName) {
 		Handler.prototype[trapName] = function () {
 			this.trapCalls.push(trapName);
+			// @ts-expect-error TODO: not sure why this is erroring
 			return Reflect[trapName].apply(Reflect, arguments);
 		};
 	});
 
 	t.test('proxy of object', function (st) {
 		var handler = new Handler();
+		// @ts-expect-error Proxy handlers can be any object
 		var proxy = new Proxy({ lastIndex: 0 }, handler);
 
 		st.equal(isRegex(proxy), false, 'proxy of plain object is not regex');
@@ -97,6 +105,7 @@ test('does not perform operations observable to Proxies', { skip: typeof Proxy !
 
 	t.test('proxy of RegExp instance', function (st) {
 		var handler = new Handler();
+		// @ts-expect-error Proxy handlers can be any object
 		var proxy = new Proxy(/a/, handler);
 
 		st.equal(isRegex(proxy), false, 'proxy of RegExp instance is not regex');

tsconfig.json

@@ -0,0 +1,9 @@
+{
+	"extends": "@ljharb/tsconfig",
+	"compilerOptions": {
+		"target": "ES2021",
+	},
+	"exclude": [
+		"coverage"
+	]
+}