ES2015 class skeleton for Polymer elements

skeleton-polymer.js

'use strict';

let behaviors = Symbol('behaviors')

const SkeletonPolymerBehavior = {
	// Define your behavior
};

class SkeletonPolymer {

	// Define behaviors with a getter
	/*
	// Simple version
	get behaviors() {
		return [SkeletonPolymerBehavior];
	}
	*/

	// Version needed when including behaviors including other behaviors
	get behaviors() {
		if (!this[behaviors]) {
			this[behaviors] = [Polymer.NeonAnimationRunnerBehavior];
		}
		return this[behaviors];
	}

	// Polymer allows a behavior to be an array or an object.
	// It flattens nested behaviors into a single array containing only objects and sets it on the prototype.
	// We need a setter to retain our flattened behaviors list
	set behaviors(value) {
		this[behaviors] = value;
	}

	// Element setup goes in beforeRegister() instead of created() callback
	beforeRegister() {
		this.is = 'skeleton-polymer';

		// To extend a native HTML element set the extends property on the prototype to the tag name of the element to extend
		// this.extends: 'input'

		// Define the properties object in beforeRegister()
		this.properties = {
			top: {
				type: String,
				value: ''
			},
			bottom: {
				type: String,
				value: ''
			}
		}

		this.listeners = {
			'neon-animation-finish': '_onNeonAnimationFinish'
		}

		// this.observers
	}

	// Define other lifecycle methods as you need
	registered() {
		// Perform one-time initialization when an element is registered (primarily useful when implementing behaviors)
	}
	created() {}
	ready() {
		this.top = this.top.toUpperCase();
		this.bottom = this.bottom.toUpperCase();
	}
	factoryImpl() {
		// Method only invoked when creating an element using the construcotr (e.g., new ABC)
		// Method not used if the element is created by markup or via document.createElement
		// Method called after the element initialisation (local DOM created, default values set, ...)
	}
	attached() {}
	detached() {}
	attributeChanged() {}
}

// Define and register the element using polymer's constructor (which returns a basic constructor)
Polymer(SkeletonPolymer);

// Set the custom element's prototype chain but not register it immediately
// It returns a constructor that can be passed to document.registerElement
// Polymer.Class(SkeletonPolymer)