chore: Add type checking

package.json

@@ -8,14 +8,15 @@
     "url": "https://github.com/btmills"
   },
   "type": "module",
-  "main": "src/index.js",
+  "main": "dist/esm/index.js",
+  "types": "dist/esm/index.d.ts",
   "exports": {
     "import": {
-      "default": "./src/index.js"
+      "default": "./dist/esm/index.js"
     }
   },
   "files": [
-    "src"
+    "dist"
   ],
   "repository": "eslint/eslint-plugin-markdown",
   "bugs": {
@@ -31,6 +32,8 @@
   ],
   "scripts": {
     "lint": "eslint .",
+    "build:dedupe-types": "node tools/dedupe-types.js dist/esm/index.js",
+    "build": "rollup -c && npm run build:dedupe-types && tsc -p tsconfig.esm.json",
     "prepare": "node ./npm-prepare.cjs",
     "release:generate:latest": "eslint-generate-release",
     "release:generate:alpha": "eslint-generate-prerelease alpha",
@@ -42,13 +45,17 @@
   "devDependencies": {
     "@eslint/core": "^0.2.0",
     "@eslint/js": "^9.4.0",
+    "@types/eslint": "^9.6.0",
     "c8": "^10.1.2",
     "chai": "^5.1.1",
     "eslint": "^9.4.0",
     "eslint-config-eslint": "^11.0.0",
     "eslint-release": "^3.1.2",
     "globals": "^15.1.0",
-    "mocha": "^10.6.0"
+    "mocha": "^10.6.0",
+    "rollup": "^4.19.0",
+    "rollup-plugin-copy": "^3.5.0",
+    "typescript": "^5.5.4"
   },
   "dependencies": {
     "mdast-util-from-markdown": "^2.0.1"

rollup.config.js

@@ -0,0 +1,10 @@
+export default {
+    input: "src/index.js",
+    output: [
+        {
+            file: "dist/esm/index.js",
+            format: "esm",
+            banner: '// @ts-self-types="./index.d.ts"'
+        }
+    ]
+};

tools/dedupe-types.js

@@ -0,0 +1,43 @@
+/**
+ * @fileoverview Strips typedef aliases from the rolled-up file. This
+ * is necessary because the TypeScript compiler throws an error when
+ * it encounters a duplicate typedef.
+ *
+ * Usage:
+ *  node scripts/strip-typedefs.js filename1.js filename2.js ...
+ *
+ * @author Nicholas C. Zakas
+ */
+
+//-----------------------------------------------------------------------------
+// Imports
+//-----------------------------------------------------------------------------
+
+import fs from "node:fs";
+
+//-----------------------------------------------------------------------------
+// Main
+//-----------------------------------------------------------------------------
+
+// read files from the command line
+const files = process.argv.slice(2);
+
+files.forEach(filePath => {
+	const lines = fs.readFileSync(filePath, "utf8").split(/\r?\n/gu);
+	const typedefs = new Set();
+
+	const remainingLines = lines.filter(line => {
+		if (!line.startsWith("/** @typedef {import")) {
+			return true;
+		}
+
+		if (typedefs.has(line)) {
+			return false;
+		}
+
+		typedefs.add(line);
+		return true;
+	});
+
+	fs.writeFileSync(filePath, remainingLines.join("\n"), "utf8");
+});

tsconfig.esm.json

@@ -0,0 +1,4 @@
+{
+  "extends": "./tsconfig.json",
+  "files": ["dist/esm/index.js"]
+}

tsconfig.json

@@ -0,0 +1,13 @@
+{
+  "files": ["src/index.js"],
+  "compilerOptions": {
+    "declaration": true,
+    "emitDeclarationOnly": true,
+    "allowJs": true,
+    "checkJs": true,
+    "outDir": "dist/esm",
+    "target": "ES2022",
+    "moduleResolution": "NodeNext",
+    "module": "NodeNext"
+  }
+}