Source: dropdown.js

/**
 * A Dropdown component - 90% UX/COE Compliant
 * <BR><BR><img src=../images/dropdown.png width=30% style="border:1px lime dashed";>
 * <BR><BR><a href="../html/dropdown.html">DEMO</a>
 */
class Dropdown extends HTMLElement {
    constructor() {
        console.group("Dropdown.constructor")
	
        super();

        console.groupEnd();
    };
    
    /**
     * Set observable values here. When Changed, attributeChangedCallback is invoked
     * @observedAttributes
     */
    static get observedAttributes() {
        console.group("Dropdown.observedAttributes");

	this.observables = ["title", "width"];
	console.log(this.observables);

        console.groupEnd();
        return this.observables;
    };

    /**
     * This function is called when this is attached to DOM
     * @connectedCallback. 
     */
    connectedCallback() {
        console.group("Dropdown.connectedCallback")
	
	let self = this;

	// MAKE SURE OUR COMPONENT HAS GLOBAL CLASS
	this.classList.add("wc");

	// FETCH ALL INTERESTING ELEMENTS
	this._fetchElements();

	// FETCH ALL ATTRIBUTES
	this._fetchAttributes();

	this.classList.add("dropdown");

	let str = "";
	str +=
	    "<button class='btn btn-default dropdown-toggle' type='button' id='" +
	    this.id + "-container' data-toggle='dropdown' aria-haspopup='true' aria-expanded='true'>" +
	    this.properties.title + " <span class='fa fa-angle-down'></span></button>" + this.dom.content;

	// REFRESH DOM NOW
	this.innerHTML = str;

	this.querySelector(".dropdown-toggle").style.width = this.properties.width;

	let tmp = this.querySelector("ul");
	tmp.classList.add("dropdown-menu");
	tmp.setAttribute("aria-labelledby", this.id + "container");

	let items = this.querySelectorAll("ul li a");
	
	// ADD CLICK CALLBACK. USER CAN IGNORE IF THE HAVE LINKS SETUP ALREAD
	for (let i=0; i<items.length; i++) {
	    let item = items[i];

	    item.addEventListener("click", function() {
		self._onClick(item);
	    });
	}

	$("#" + this.id + " .dropdown-menu").on('click', 'li a', function(){
	    
            $(this).parent().parent().siblings(".btn:first-child").html($(this).text() + "<span class='fa fa-angle-down'></span>");
            $(this).parent().parent().siblings(".btn:first-child").val($(this).text());
	});

	// WRAP UP AND ADD STATS
	this._finalize();

	// SHOW IT NOW (NO FLICKERS) 
	this.style.visibility = "visible";

        console.groupEnd();
    };

    /**
     * Invoked When component is removed. Usually with a .remove() function call
     * @disconnectedCallback
     */
    disconnectedCallback() {
        console.group("Dropdown.disconnectedCallback")

	/* CLEAN UP NOW */

        console.groupEnd();
    };

    /**
     * Called with .setAttribute(...) function call
     * @attributeChangedCallback
     */
    attributeChangedCallback(attr, oldval, newval) {
        console.group("Dropdown.attributeChangedCallback:", attr, oldval, newval);

	this.properties = this.properties || [];

	// EXAMPLE ONLY. replace with observables
	switch(attr)
	{
	    case "title":
	    this.properties.title = newval;
	    this.style.title = this.properties.title;
	    break;

	    case "width":
	    this.properties.width = newval;
	    this.style.width = this.properties.width;
	    break;
	}
	
        console.groupEnd();
    };

    /**
     * Stores DOM elements of interest for future use
     * @_fetchElements
     */
    _fetchElements() {
	console.group("Dropdown._fetchElements");
	
	this.dom = this.dom || [];
	this.dom.content = this.innerHTML;

	console.groupEnd();
    };

    /**
     * Component attributes are _fetched and defaults are set if undefined
     * @_fetchAttributes
     * @param {string} [width=auto] width of dropdown button
     */
    _fetchAttributes() {
	console.group("Dropdown._fetchAttributes");

	this.properties = {
	    "cname"   : "Dropdown",
	    "author"  : "Mel Heravi",
	    "version" : "1.0",
	    "title"   : "NOT SET",
	    "width"   : "auto"
	};

	if (this.hasAttribute("title")) {
	    this.properties.title = this.getAttribute("title");
	    console.log("title: ", this.properties.title);
	}

	if (this.hasAttribute("width")) {
	    this.properties.width = this.getAttribute("width");
	    console.log("width: ", this.properties.width);
	}

	console.groupEnd();
    };

    /**
     * A sample callback usage function - see connectedCallback()
     * @_onClick
     * @param {object} item link that was clicked on
     */
    _onClick(item) {
	console.group("Dropdown._onClick:", item);

	//PUBLISH TO THE EVENT
	wc.publish(this, "wc-tabs", {
	    item: item,
	    action: "click"
	});

	console.groupEnd();
    };

    /**
     * Destroy the instance object and artifacts
     * @_destroy
     */
    destroy() {
	console.group("Message.destroy:", this.id);

	// FREE POINTER
	delete this;

	// REMOVE ITEM FROM DOM
	this.parentNode.removeChild(this);

	console.groupEnd();
    };
    /**
     * SAVE DATA FOR ANALYTICS
     * @__finalize
     */
    _finalize() {
	console.group("Dropdown._finalize:", this.id);

	this.classList.add("wc");

	// ADD ANALYTICS HERE
	wc.getStats(this, this.properties.cname, this.properties.version);
	
	console.groupEnd();
    };

    /**
     * FOR TESTING PURPOSES
     * @test
     */
    static test() {
	console.group("Dropdown.test");

	console.log("testing results will be printed here...");

	console.groupEnd();
	return true;
    }
}

window.customElements.define('wc-dropdown', Dropdown);