add types

index.d.ts

@@ -0,0 +1,3 @@
+declare function isMap<K = unknown, V = unknown>(x: unknown): x is Map<K, V>;
+
+export = isMap;

index.js

@@ -1,11 +1,13 @@
 'use strict';
 
+/** @const */
 var $Map = typeof Map === 'function' && Map.prototype ? Map : null;
 var $Set = typeof Set === 'function' && Set.prototype ? Set : null;
 
 var exported;
 
 if (!$Map) {
+	/** @type {import('.')} */
 	// eslint-disable-next-line no-unused-vars
 	exported = function isMap(x) {
 		// `Map` is not present in this environment.
@@ -16,13 +18,15 @@ if (!$Map) {
 var $mapHas = $Map ? Map.prototype.has : null;
 var $setHas = $Set ? Set.prototype.has : null;
 if (!exported && !$mapHas) {
+	/** @type {import('.')} */
 	// eslint-disable-next-line no-unused-vars
 	exported = function isMap(x) {
 		// `Map` does not have a `has` method
 		return false;
 	};
 }
 
+/** @type {import('.')} */
 module.exports = exported || function isMap(x) {
 	if (!x || typeof x !== 'object') {
 		return false;
@@ -36,6 +40,7 @@ module.exports = exported || function isMap(x) {
 				return true;
 			}
 		}
+		// @ts-expect-error TS can't figure out that $Map is always truthy here
 		return x instanceof $Map; // core-js workaround, pre-v2.5.0
 	} catch (e) {}
 	return false;

package.json

@@ -12,6 +12,7 @@
 		"prepublish": "not-in-publish || npm run prepublishOnly",
 		"pretest": "npm run lint",
 		"lint": "eslint --ext=js,mjs .",
+		"postlint": "tsc -p . && attw -P",
 		"tests-only": "nyc tape 'test/**/*.js'",
 		"tests:shims": "nyc tape --require=es5-shim --require=es5-shim 'test/**/*.js'",
 		"tests:corejs": "nyc tape --require=core-js 'test/**/*.js'",
@@ -39,7 +40,11 @@
 	},
 	"homepage": "https://github.com/inspect-js/is-map#readme",
 	"devDependencies": {
+		"@arethetypeswrong/cli": "^0.15.0",
 		"@ljharb/eslint-config": "^21.1.0",
+		"@types/for-each": "^0.3.3",
+		"@types/object-inspect": "^1.8.4",
+		"@types/tape": "^5.6.4",
 		"aud": "^2.0.4",
 		"auto-changelog": "^2.4.0",
 		"core-js": "^2.6.12",
@@ -52,7 +57,8 @@
 		"nyc": "^10.3.2",
 		"object-inspect": "^1.13.1",
 		"safe-publish-latest": "^2.0.0",
-		"tape": "^5.7.5"
+		"tape": "^5.7.5",
+		"typescript": "^5.5.0-dev.20240308"
 	},
 	"auto-changelog": {
 		"output": "CHANGELOG.md",

tsconfig.json

@@ -0,0 +1,49 @@
+{
+  "compilerOptions": {
+    /* Visit https://aka.ms/tsconfig to read more about this file */
+
+    /* Projects */
+
+    /* Language and Environment */
+    "target": "ESNext",                                  /* Set the JavaScript language version for emitted JavaScript and include compatible library declarations. */
+    // "lib": [],                                        /* Specify a set of bundled library declaration files that describe the target runtime environment. */
+    // "noLib": true,                                    /* Disable including any library files, including the default lib.d.ts. */
+    "useDefineForClassFields": true,                     /* Emit ECMAScript-standard-compliant class fields. */
+    // "moduleDetection": "auto",                        /* Control what method is used to detect module-format JS files. */
+
+    /* Modules */
+    "module": "commonjs",                                /* Specify what module code is generated. */
+    // "rootDir": "./",                                  /* Specify the root folder within your source files. */
+    // "moduleResolution": "node10",                     /* Specify how TypeScript looks up a file from a given module specifier. */
+    // "baseUrl": "./",                                  /* Specify the base directory to resolve non-relative module names. */
+    // "paths": {},                                      /* Specify a set of entries that re-map imports to additional lookup locations. */
+    // "rootDirs": [],                                   /* Allow multiple folders to be treated as one when resolving modules. */
+    "typeRoots": ["types"],                              /* Specify multiple folders that act like './node_modules/@types'. */
+    "resolveJsonModule": true,                           /* Enable importing .json files. */
+    // "allowArbitraryExtensions": true,                 /* Enable importing files with any extension, provided a declaration file is present. */
+
+    /* JavaScript Support */
+    "allowJs": true,                                     /* Allow JavaScript files to be a part of your program. Use the 'checkJS' option to get errors from these files. */
+    "checkJs": true,                                     /* Enable error reporting in type-checked JavaScript files. */
+    "maxNodeModuleJsDepth": 0,                           /* Specify the maximum folder depth used for checking JavaScript files from 'node_modules'. Only applicable with 'allowJs'. */
+
+    /* Emit */
+    "declaration": true,                                 /* Generate .d.ts files from TypeScript and JavaScript files in your project. */
+    "declarationMap": true,                              /* Create sourcemaps for d.ts files. */
+    "noEmit": true,                                      /* Disable emitting files from a compilation. */
+
+    /* Interop Constraints */
+    "allowSyntheticDefaultImports": true,                /* Allow 'import x from y' when a module doesn't have a default export. */
+    "esModuleInterop": true,                             /* Emit additional JavaScript to ease support for importing CommonJS modules. This enables 'allowSyntheticDefaultImports' for type compatibility. */
+    "forceConsistentCasingInFileNames": true,            /* Ensure that casing is correct in imports. */
+
+    /* Type Checking */
+    "strict": true,                                      /* Enable all strict type-checking options. */
+
+    /* Completeness */
+    //"skipLibCheck": true                                 /* Skip type checking all .d.ts files. */
+  },
+  "exclude": [
+    "coverage"
+  ]
+}