[New] add types

index.d.ts

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

index.js

@@ -3,9 +3,12 @@
 var isSymbol = require('is-symbol');
 var callBound = require('call-bind/callBound');
 
+/** @type {typeof Symbol.keyFor} */
 var keyFor = callBound('Symbol.keyFor', true);
+/** @type {(receiver: ThisParameterType<typeof Symbol.prototype.valueOf>, ...args: Parameters<typeof Symbol.prototype.valueOf>) => ReturnType<typeof Symbol.prototype.valueOf>} */
 var symbolValueOf = callBound('Symbol.prototype.valueOf', true);
 
+/** @type {import('.')} */
 module.exports = function isRegisteredSymbol(sym) {
 	if (!isSymbol(sym)) {
 		return false;

package.json

@@ -18,6 +18,7 @@
 		"posttest": "npx npm@'>=10.2' audit --production",
 		"prelint": "evalmd README.md",
 		"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)\")\""
 	},
@@ -47,7 +48,15 @@
 		"is-symbol": "^1.0.4"
 	},
 	"devDependencies": {
+		"@arethetypeswrong/cli": "^0.17.0",
 		"@ljharb/eslint-config": "^21.1.1",
+		"@ljharb/tsconfig": "^0.2.0",
+		"@types/call-bind": "^1.0.5",
+		"@types/for-each": "^0.3.3",
+		"@types/has-symbols": "^1.0.2",
+		"@types/is-symbol": "^1.0.2",
+		"@types/object-inspect": "^1.13.0",
+		"@types/tape": "^5.6.4",
 		"auto-changelog": "^2.5.0",
 		"encoding": "^0.1.13",
 		"es-value-fixtures": "^1.5.0",
@@ -60,7 +69,8 @@
 		"nyc": "^10.3.2",
 		"object-inspect": "^1.13.3",
 		"safe-publish-latest": "^2.0.0",
-		"tape": "^5.9.0"
+		"tape": "^5.9.0",
+		"typescript": "^5.8.0-dev.20241125"
 	},
 	"testling": {
 		"files": "test/index.js"

test/index.js

@@ -12,7 +12,11 @@ test('isRegisteredSymbol', function (t) {
 	t.equal(typeof isRegisteredSymbol, 'function', 'is a function');
 
 	t.test('non-symbols', function (st) {
-		forEach(v.nonSymbolPrimitives.concat(v.objects), function (nonSymbol) {
+		forEach([].concat(
+			// @ts-expect-error TS sucks with concat
+			v.nonSymbolPrimitives,
+			v.objects
+		), function (nonSymbol) {
 			st.equal(isRegisteredSymbol(nonSymbol), false, inspect(nonSymbol) + ' is not a Symbol');
 		});
 

tsconfig.json

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