Userscript to add auto-refresh functionality to GMail Classic

gmail_classic.user.js

// ==UserScript==
// @name         GMail Classic
// @namespace    https://prahladyeri.com
// @version      0.1
// @description  Add refresh timer to GMail Classic
// @author       Prahlad Yeri
// @match        https://mail.google.com/*
// @require http://ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js
// @grant        none
// ==/UserScript==

(function() {
    'use strict';
	var seconds = 300; //5 mins
	var interval = seconds * 1000;
	var remaining = interval;
	
	var btn = document.createElement("button");
	btn.id = 'btnRefresh';
	btn.textContent = "Refresh (" + (remaining/1000) + " seconds)";
	btn.onclick = function() {
		window.location = location;
	}
	$("div#gbar").append(btn);
	setInterval(refreshMe, interval);
	setInterval(function(){
		remaining = remaining - 1000;
		btn.textContent = "Refresh (" + (remaining/1000) + " seconds)";
	}, 1000);
	
	//
	function refreshMe() {
		window.location = window.location;
	}

})();