Sets and retrieves a key to select user UI color preference

simple-localstorage.js

/* Arthem Co. 
 * Let "doot" be a reserved private variable.
 *
 * Michael Hemingway 2016 
 */

(function () {
	'use strict';

	// HELPER FUNCTIONS
	var $ = function (id) {
		return document.getElementById(id);
	};

	function setStorage() {
		var a = localStorage.getItem('dark-ui'),
		    body = document.getElementsByTagName('body')[0],
		    toggle = document.getElementById("dark-ui-toggle");
		if (a === "dark") {
			body.className += (' dark-ui');
			toggle.checked = true;
		} else {
			body.classList.remove('dark-ui');
			toggle.checked = false;
		}
	}

	// read key and apply/remove class with setStorage method.
	document.addEventListener("DOMContentLoaded", function (event) {

		$('dark-ui-toggle').addEventListener("click", function () {
			var b = $('dark-ui-toggle'),
					s = b.checked;
			if (s !== true) {
				b.checked = false;
				localStorage.setItem('dark-ui', 'light');
			} else {
				b.checked = true;
				localStorage.setItem('dark-ui', 'dark');
			}
			setStorage();
		});
		setStorage();
	});
	
}());