add barebones typescript config

package.json

@@ -41,6 +41,7 @@
     "mocha": "^10.3.0",
     "node-fetch": "^3.3.2",
     "rollup-plugin-terser": "^7.0.2",
+    "typescript": "^5.4.5",
     "yauzl-promise": "^4.0.0"
   },
   "license": "MPL-2.0",

tsconfig.json

@@ -0,0 +1,15 @@
+{
+  "include": ["dist/ical.js"],
+  "compilerOptions": {
+    // Tells TypeScript to read JS files, as
+    // normally they are ignored as source files
+    "allowJs": true,
+    // Generate d.ts files
+    "declaration": true,
+    // only output d.ts files
+    "emitDeclarationOnly": true,
+    // go to js file when using IDE functions like
+    // "Go to Definition" in VSCode
+    "declarationMap": true
+  }
+}