[New] add types

.gitignore

@@ -109,3 +109,6 @@ package-lock.json
 yarn.lock
 
 .npmignore
+
+*.d.ts
+*.d.ts.map

index.js

@@ -11,26 +11,34 @@ var $slice = callBound('Array.prototype.slice');
 var hasSymbols = require('has-symbols/shams')();
 var isConcatSpreadable = hasSymbols && Symbol.isConcatSpreadable;
 
-var empty = [];
+/** @type {never[]} */ var empty = [];
 var $concatApply = isConcatSpreadable ? callBind.apply($concat, empty) : null;
-var $concatCall = isConcatSpreadable ? null : callBind($concat, empty);
 
 var isArray = isConcatSpreadable ? require('isarray') : null;
 
-module.exports = isConcatSpreadable
+/** @type {typeof Array.prototype.concat} */
+var safeConcat = isConcatSpreadable
 	// eslint-disable-next-line no-unused-vars
 	? function safeArrayConcat(item) {
 		for (var i = 0; i < arguments.length; i += 1) {
-			var arg = arguments[i];
+			/** @type {typeof item} */ var arg = arguments[i];
+			// @ts-expect-error ts(2538) see https://github.com/microsoft/TypeScript/issues/9998#issuecomment-1890787975; works if `const`
 			if (arg && typeof arg === 'object' && typeof arg[isConcatSpreadable] === 'boolean') {
+				// @ts-expect-error ts(7015) TS doesn't yet support Symbol indexing
 				if (!empty[isConcatSpreadable]) {
+					// @ts-expect-error ts(7015) TS doesn't yet support Symbol indexing
 					empty[isConcatSpreadable] = true;
 				}
-				var arr = isArray(arg) ? $slice(arg) : [arg];
+				// @ts-expect-error ts(2721) ts(18047) not sure why TS can't figure out this can't be nul
+				/** @type {T[]} */ var arr = isArray(arg) ? $slice(arg) : [arg];
+				// @ts-expect-error ts(7015) TS can't handle expandos on an array
 				arr[isConcatSpreadable] = true; // shadow the property. TODO: use [[Define]]
 				arguments[i] = arr;
 			}
 		}
+		// @ts-expect-error ts(2345) TS doesn't understand that apply can take an arguments object
 		return $concatApply(arguments);
 	}
-	: $concatCall;
+	: callBind($concat, empty);
+
+module.exports = safeConcat;

package.json

@@ -9,10 +9,14 @@
 	},
 	"sideEffects": false,
 	"scripts": {
-		"prepack": "npmignore --auto --commentLines=autogenerated",
+		"prepack": "npmignore --auto --commentLines=autogenerated && npm run emit",
 		"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)\")\"",
+		"prelint": "npm run tsc",
 		"lint": "eslint --ext=js,mjs .",
+		"preemit": "rm -f *.ts *.ts.map test/*.ts test/*.ts.map",
+		"emit": "npm run tsc -- --noEmit false --emitDeclarationOnly",
+		"tsc": "tsc -p .",
 		"postlint": "evalmd README.md",
 		"prepublish": "not-in-publish || npm run prepublishOnly",
 		"prepublishOnly": "safe-publish-latest",
@@ -43,6 +47,12 @@
 	"homepage": "https://github.com/ljharb/safe-array-concat#readme",
 	"devDependencies": {
 		"@ljharb/eslint-config": "^21.1.0",
+		"@types/call-bind": "^1.0.5",
+		"@types/get-intrinsic": "^1.2.2",
+		"@types/has-symbols": "^1.0.2",
+		"@types/isarray": "^2.0.2",
+		"@types/mock-property": "^1.0.2",
+		"@types/tape": "^5.6.4",
 		"aud": "^2.0.4",
 		"auto-changelog": "^2.4.0",
 		"eslint": "=8.8.0",
@@ -53,7 +63,8 @@
 		"nyc": "^10.3.2",
 		"safe-publish-latest": "^2.0.0",
 		"set-function-length": "^1.2.0",
-		"tape": "^5.7.3"
+		"tape": "^5.7.3",
+		"typescript": "^5.4.0-dev.20240114"
 	},
 	"dependencies": {
 		"call-bind": "^1.0.5",
@@ -71,7 +82,9 @@
 	},
 	"publishConfig": {
 		"ignore": [
-			".github/workflows"
+			".github/workflows",
+			"!*.d.ts",
+			"!*.d.ts.map"
 		]
 	},
 	"engines": {

test/index.js

@@ -15,8 +15,7 @@ test('safe-array-concat', function (t) {
 	t.equal(
 		safeConcat.length,
 		boundFnsHaveConfigurableLengths ? 1 : 0,
-		'has a length of ' + (boundFnsHaveConfigurableLengths ? 1 : '0 (function lengths are not configurable)'),
-		'length is as expected'
+		'has a length of ' + (boundFnsHaveConfigurableLengths ? 1 : '0 (function lengths are not configurable)')
 	);
 
 	t.deepEqual(
@@ -48,7 +47,9 @@ test('safe-array-concat', function (t) {
 
 	t.test('has Symbol.species', { skip: !species }, function (st) {
 		var speciesArr = [1, 2];
+		// @ts-expect-error ts(2740) TS's `constructor` type requires a function
 		speciesArr.constructor = {};
+		// @ts-expect-error ts(2538) TS can't type narrow from tape's `skip`
 		speciesArr.constructor[species] = function Species() {
 			return { args: arguments };
 		};
@@ -63,24 +64,28 @@ test('safe-array-concat', function (t) {
 	});
 
 	t.test('has isConcatSpreadable', { skip: !isConcatSpreadable }, function (st) {
-		st.teardown(mockProperty(String.prototype, isConcatSpreadable, { value: true }));
-
-		var nonSpreadable = [1, 2];
-		nonSpreadable[isConcatSpreadable] = false;
-
-		st.deepEqual(
-			safeConcat(nonSpreadable, 3, 4, 'foo', Object('bar')),
-			[1, 2, 3, 4, 'foo', Object('bar')],
-			'a non-concat-spreadable array is spreaded, and a concat-spreadable String is not spreaded'
-		);
-
-		st.teardown(mockProperty(Array.prototype, isConcatSpreadable, { value: false }));
-
-		st.deepEqual(
-			safeConcat([1, 2], 3, 4, 'foo', Object('bar')),
-			[1, 2, 3, 4, 'foo', Object('bar')],
-			'all arrays marked non-concat-spreadable are still spreaded, and a concat-spreadable String is not spreaded'
-		);
+		// TS can't type narrow from tape's `skip`
+		if (isConcatSpreadable) {
+			st.teardown(mockProperty(String.prototype, isConcatSpreadable, { value: true }));
+
+			var nonSpreadable = [1, 2];
+			// @ts-expect-error ts(7015) TS can't handle expandos on an array
+			nonSpreadable[isConcatSpreadable] = false;
+
+			st.deepEqual(
+				safeConcat(nonSpreadable, 3, 4, 'foo', Object('bar')),
+				[1, 2, 3, 4, 'foo', Object('bar')],
+				'a non-concat-spreadable array is spreaded, and a concat-spreadable String is not spreaded'
+			);
+
+			st.teardown(mockProperty(Array.prototype, isConcatSpreadable, { value: false }));
+
+			st.deepEqual(
+				safeConcat([1, 2], 3, 4, 'foo', Object('bar')),
+				[1, 2, 3, 4, 'foo', Object('bar')],
+				'all arrays marked non-concat-spreadable are still spreaded, and a concat-spreadable String is not spreaded'
+			);
+		}
 
 		st.end();
 	});

tsconfig.json

@@ -0,0 +1,49 @@
+{
+  "compilerOptions": {
+    /* Visit https://aka.ms/tsconfig.json to read more about this file */
+
+    /* Projects */
+
+    /* Language and Environment */
+    "target": "es2022",                                  /* 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": "node",                       /* 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": 1,                           /* 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",
+  ],
+}