diff --git a/CONFIG.md b/CONFIG.md
deleted file mode 100644
index 7165def..0000000
--- a/CONFIG.md
+++ /dev/null
@@ -1,74 +0,0 @@
-# config.json format
-
-This document describes the field in config.json.
-
-Create config.json by running:
-
-`cp example.config.json config.json`
-
-in the project folder, then edit it.
-
-## "master"
-
-`number|string`
-
-Master admin ID as a number or username as a string.
-
-## "token"
-
-`string`
-
-Telegram Bot token obtained from [https://t.me/BotFather](@BotFather).
-
-## "plugins"
-
-`[string]`
-
-List of plugin names to be loaded.
-
-## "deleteCommands"
-
-`string`
-
-Which messages with commands should be deleted?
-
-Options:
-
-* "all"
-* "own" (default) - leave commands meant for other bots
-* "none"
-
-## "numberOfWarnsToBan"
-
-`number`
-
-Number of warns that will get someone banned.
-
-## "groupsInlineKeyboard"
-
-`[[inlineButton]]`
-
-inline keyboard to be added to reply to /groups.
-
-## "warnInlineKeyboard"
-
-`[[inlineButton]]`
-
-Inline keyboard to be added to warn message.
-
-## "excludedChannels"
-
-`[string]`
-
-List of channels that you want to be excluded from automatic warns.
-
-Use `"*"` to disable.
-
-## "excludedGroups"
-
-`[string]`
-
-List of groups that you want to be excluded from automatic warns.
-
-Use `"*"` to disable.
-
diff --git a/README.md b/README.md
index c70bc4f..bc9ad1b 100644
--- a/README.md
+++ b/README.md
@@ -14,7 +14,7 @@ You need [Node.js](https://nodejs.org/) (> 8.1) to run this bot.
 1. Create a bot via [@BotFather](https://t.me/BotFather) and grab a **token**.
 2. Clone this repository or [download zip](https://github.com/TheDevs-Network/the-guard-bot/archive/master.zip).
 3. Install dependencies via `npm install`.
-4. Copy `config.example.json` to `config.json`, fill it properly and remove comments.
+4. Copy `example.config.js` to `config.js` and edit it.
 5. Start the bot via `npm start`.
 
 Now you can add the bot as **administrator** to your groups.
diff --git a/example.config.js b/example.config.js
new file mode 100644
index 0000000..8dc539e
--- /dev/null
+++ b/example.config.js
@@ -0,0 +1,71 @@
+'use strict';
+
+/*
+ * Create `config.js` by running `cp example.config.js config.js`
+ * in the project folder, then edit it.
+ *
+ * Config file in JSON format (`config.json`) is also supported.
+ * For backwards compatibility, and because why not, it needs no extra code.
+ */
+
+module.exports = {
+
+	/**
+	 * @type {!( number | string )}
+	 * ID (number) or username (string) of master,
+	 * the person who can promote and demote admins,
+	 * and add the bot to groups.
+	 */
+	master: 123456789,
+
+	/**
+	 * @type {!string}
+	 * Telegram Bot token obtained from https://t.me/BotFather.
+	 */
+	token: '',
+
+
+	/**
+	 * @type {( 'all' | 'own' | 'none' )}
+	 * Which messages with commands should be deleted?
+	 * Defaults to 'own' -- don't delete commands meant for other bots.
+	 */
+	deleteCommands: 'own', // eslint-disable-line sort-keys
+
+	/**
+	 * @type {( number | string | false )}
+	 * Timeout before removing join and leave messages.
+	 * String to be parsed by https://npmjs.com/millisecond,
+	 * or number of milliseconds.
+	 * Pass 0 to remove immediately.
+	 * Pass false to never remove.
+	 */
+	deleteJoinsAfter: '2 minutes',
+
+	excludeLinks: [],
+
+	/**
+	 * @type {InlineKeyboardMarkup}
+	 * Inline keyboard to be added to reply to /groups.
+	 * We use it to display button opening our webpage.
+	 */
+	groupsInlineKeyboard: [],
+
+	numberOfWarnsToBan: 3,
+
+	/**
+	 * @type {string[]}
+	 * List of plugin names to be loaded.
+	 * See Readme in plugins directory for more details.
+	 */
+	plugins: [],
+
+	/**
+	 * @type {InlineKeyboardMarkup}
+	 * Inline keyboard to be added to warn message.
+	 * We use it to display button showing our rules.
+	 */
+	warnInlineKeyboard: [],
+};
+
+Object.freeze(module.exports);
diff --git a/example.config.json b/example.config.json
deleted file mode 100644
index cc00f95..0000000
--- a/example.config.json
+++ /dev/null
@@ -1,11 +0,0 @@
-{
-	"master": 123456789,
-	"token": "",
-	"plugins": [],
-	"deleteCommands": "own",
-	"deleteJoinsAfter": "2 minutes",
-	"numberOfWarnsToBan": 3,
-	"groupsInlineKeyboard": [],
-	"warnInlineKeyboard": [],
-	"excludeLinks": []
-}