[New] add types

index.d.ts

@@ -0,0 +1,3 @@
+declare function isString(value: unknown): value is string | String;
+
+export = isString;

index.js

@@ -2,8 +2,10 @@
 
 var callBound = require('call-bind/callBound');
 
+/** @type {(receiver: ThisParameterType<typeof String.prototype.valueOf>, ...args: Parameters<typeof String.prototype.valueOf>) => ReturnType<typeof String.prototype.valueOf>} */
 var $strValueOf = callBound('String.prototype.valueOf');
 
+/** @type {import('.')} */
 var tryStringObject = function tryStringObject(value) {
 	try {
 		$strValueOf(value);
@@ -12,10 +14,12 @@ var tryStringObject = function tryStringObject(value) {
 		return false;
 	}
 };
+/** @type {(receiver: ThisParameterType<typeof Object.prototype.toString>, ...args: Parameters<typeof Object.prototype.toString>) => ReturnType<typeof Object.prototype.toString>} */
 var $toString = callBound('Object.prototype.toString');
 var strClass = '[object String]';
 var hasToStringTag = require('has-tostringtag/shams')();
 
+/** @type {import('.')} */
 module.exports = function isString(value) {
 	if (typeof value === 'string') {
 		return true;

package.json

@@ -19,6 +19,7 @@
 		"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)\")\""
 	},
@@ -39,7 +40,12 @@
 		"has-tostringtag": "^1.0.2"
 	},
 	"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/tape": "^5.6.5",
 		"auto-changelog": "^2.5.0",
 		"core-js": "^3.39.0",
 		"eclint": "^2.8.1",
@@ -50,7 +56,8 @@
 		"npmignore": "^0.3.1",
 		"nyc": "^10.3.2",
 		"safe-publish-latest": "^2.0.0",
-		"tape": "^5.9.0"
+		"tape": "^5.9.0",
+		"typescript": "next"
 	},
 	"testling": {
 		"files": "test/index.js",

test/index.js

@@ -5,6 +5,7 @@ var isString = require('../');
 var hasToStringTag = require('has-tostringtag/shams')();
 
 test('not Strings', function (t) {
+	// @ts-expect-error
 	t.notOk(isString(), 'undefined is not String');
 	t.notOk(isString(null), 'null is not String');
 	t.notOk(isString(false), 'false is not String');
@@ -23,6 +24,7 @@ test('not Strings', function (t) {
 });
 
 test('@@toStringTag', { skip: !hasToStringTag }, function (t) {
+	/** @type {{ toString(): unknown; valueOf(): unknown; [Symbol.toStringTag]?: string; }} */
 	var fakeString = {
 		toString: function () { return '7'; },
 		valueOf: function () { return '42'; }

tsconfig.json

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