[New] add types

index.d.ts

@@ -0,0 +1,3 @@
+declare function hasNativeSymbols(): boolean;
+
+export = hasNativeSymbols;

index.js

@@ -3,6 +3,7 @@
 var origSymbol = typeof Symbol !== 'undefined' && Symbol;
 var hasSymbolSham = require('./shams');
 
+/** @type {import('.')} */
 module.exports = function hasNativeSymbols() {
 	if (typeof origSymbol !== 'function') { return false; }
 	if (typeof Symbol !== 'function') { return false; }

package.json

@@ -17,6 +17,7 @@
 		"test:shams:corejs": "nyc node test/shams/core-js.js",
 		"test:shams:getownpropertysymbols": "nyc node test/shams/get-own-property-symbols.js",
 		"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)\")\""
 	},
@@ -55,7 +56,11 @@
 	},
 	"homepage": "https://github.com/ljharb/has-symbols#readme",
 	"devDependencies": {
+		"@arethetypeswrong/cli": "^0.17.0",
 		"@ljharb/eslint-config": "^21.1.1",
+		"@ljharb/tsconfig": "^0.2.0",
+		"@types/core-js": "^2.5.8",
+		"@types/tape": "^5.6.5",
 		"auto-changelog": "^2.5.0",
 		"core-js": "^2.6.12",
 		"encoding": "^0.1.13",
@@ -65,7 +70,8 @@
 		"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",
@@ -98,7 +104,8 @@
 	},
 	"publishConfig": {
 		"ignore": [
-			".github/workflows"
+			".github/workflows",
+			"types"
 		]
 	}
 }

shams.d.ts

@@ -0,0 +1,3 @@
+declare function hasSymbolShams(): boolean;
+
+export = hasSymbolShams;

shams.js

@@ -1,10 +1,12 @@
 'use strict';
 
+/** @type {import('./shams')} */
 /* eslint complexity: [2, 18], max-statements: [2, 33] */
 module.exports = function hasSymbols() {
 	if (typeof Symbol !== 'function' || typeof Object.getOwnPropertySymbols !== 'function') { return false; }
 	if (typeof Symbol.iterator === 'symbol') { return true; }
 
+	/** @type {{ [k in symbol]?: unknown }} */
 	var obj = {};
 	var sym = Symbol('test');
 	var symObj = Object(sym);
@@ -23,7 +25,7 @@ module.exports = function hasSymbols() {
 
 	var symVal = 42;
 	obj[sym] = symVal;
-	for (sym in obj) { return false; } // eslint-disable-line no-restricted-syntax, no-unreachable-loop
+	for (var _ in obj) { return false; } // eslint-disable-line no-restricted-syntax, no-unreachable-loop
 	if (typeof Object.keys === 'function' && Object.keys(obj).length !== 0) { return false; }
 
 	if (typeof Object.getOwnPropertyNames === 'function' && Object.getOwnPropertyNames(obj).length !== 0) { return false; }
@@ -34,7 +36,8 @@ module.exports = function hasSymbols() {
 	if (!Object.prototype.propertyIsEnumerable.call(obj, sym)) { return false; }
 
 	if (typeof Object.getOwnPropertyDescriptor === 'function') {
-		var descriptor = Object.getOwnPropertyDescriptor(obj, sym);
+		// eslint-disable-next-line no-extra-parens
+		var descriptor = /** @type {PropertyDescriptor} */ (Object.getOwnPropertyDescriptor(obj, sym));
 		if (descriptor.value !== symVal || descriptor.enumerable !== true) { return false; }
 	}
 

test/shams/core-js.js

@@ -8,6 +8,7 @@ if (typeof Symbol === 'function' && typeof Symbol() === 'symbol') {
 		t.equal(typeof Symbol(), 'symbol');
 		t.end();
 	});
+	// @ts-expect-error TS is stupid and doesn't know about top level return
 	return;
 }
 

test/shams/get-own-property-symbols.js

@@ -8,6 +8,7 @@ if (typeof Symbol === 'function' && typeof Symbol() === 'symbol') {
 		t.equal(typeof Symbol(), 'symbol');
 		t.end();
 	});
+	// @ts-expect-error TS is stupid and doesn't know about top level return
 	return;
 }
 

test/tests.js

@@ -1,5 +1,6 @@
 'use strict';
 
+/** @type {(t: import('tape').Test) => false | void} */
 // eslint-disable-next-line consistent-return
 module.exports = function runSymbolTests(t) {
 	t.equal(typeof Symbol, 'function', 'global Symbol is a function');
@@ -31,6 +32,7 @@ module.exports = function runSymbolTests(t) {
 
 	t.equal(typeof Object.getOwnPropertySymbols, 'function', 'Object.getOwnPropertySymbols is a function');
 
+	/** @type {{ [k in symbol]?: unknown }} */
 	var obj = {};
 	var sym = Symbol('test');
 	var symObj = Object(sym);
@@ -40,8 +42,8 @@ module.exports = function runSymbolTests(t) {
 
 	var symVal = 42;
 	obj[sym] = symVal;
-	// eslint-disable-next-line no-restricted-syntax
-	for (sym in obj) { t.fail('symbol property key was found in for..in of object'); }
+	// eslint-disable-next-line no-restricted-syntax, no-unused-vars
+	for (var _ in obj) { t.fail('symbol property key was found in for..in of object'); }
 
 	t.deepEqual(Object.keys(obj), [], 'no enumerable own keys on symbol-valued object');
 	t.deepEqual(Object.getOwnPropertyNames(obj), [], 'no own names on symbol-valued object');

tsconfig.json

@@ -0,0 +1,10 @@
+{
+	"extends": "@ljharb/tsconfig",
+	"compilerOptions": {
+		"target": "ES2021",
+		"maxNodeModuleJsDepth": 0,
+	},
+	"exclude": [
+		"coverage"
+	]
+}

types/get-own-property-symbols/index.d.ts

@@ -0,0 +1,3 @@
+declare module 'get-own-property-symbols' {
+    export {}
+}