test(lint): Fix linting issues

.eslintignore

@@ -0,0 +1 @@
+build/

.eslintrc.json

@@ -1,19 +1,14 @@
 {
-  "extends": ["eslint:recommended", "plugin:prettier/recommended"],
+  "parser": "@typescript-eslint/parser",
+  "plugins": ["@typescript-eslint"],
+  "extends": [
+    "eslint:recommended",
+    "plugin:@typescript-eslint/recommended",
+    "prettier/@typescript-eslint",
+    "plugin:prettier/recommended"
+  ],
   "env": {"node": true, "browser": true},
   "rules": {
     "no-trailing-spaces": ["error"]
-  },
-  "overrides": [
-    {
-      "files": ["test/*.js"],
-      "env": {
-        "node": true,
-        "es6": true
-      },
-      "parserOptions": {
-        "sourceType": "module"
-      }
-    }
-  ]
+  }
 }

src/cli.ts

@@ -14,8 +14,7 @@ interface Ical2JsonOptions {
  * @param {Object} options
  * @return {Promise}
  */
-export default function (options: Ical2JsonOptions) {
-  const filePromises = [];
+export default function (options: Ical2JsonOptions): boolean {
   const files = options.args || [];
 
   for (let i = 0; i < files.length; i++) {

src/ical2json.ts

@@ -76,7 +76,7 @@ function convert(source: string): IcalObject {
 function revert(object: IcalObject): string {
   const lines = [];
 
-  for (let key in object) {
+  for (const key in object) {
     const value = object[key];
     if (Array.isArray(value)) {
       if (key === 'RDATE') {