Spark AR Firebase sharing the state tutorial.

spark-ar-firebase.js

// -- Firebase

const Firebase = (function () {
	// -- Modules

	const D = require("Diagnostics");
	const N = require("Networking");

	// -- Public

	/**
	 * Firebase class.
	 * 
	 * @constructor
	 * @param {String} url - The url of your realtime database.
	 */
	function Firebase(url) {
		this._url = url;
		this._isObserving = false;
		this._onUpdate = null;
	}

	/**
	 * Update the realtime database and set the data as current value.
	 */
	Firebase.prototype.set = function(data) {
		let options = {
			method: 'PUT', 
			body: JSON.stringify(data)
		}

		N.fetch(this._url, options).then(function(result) {
			if (!((result.status >= 200) && (result.status < 300))) {
				D.log("Failed to post data!");
			}
		});
	}

	/**
	 * Update the realtime database and set the data as current value.
	 */
	Firebase.prototype.subscribe = function(onUpdate) {
		this._onUpdate = onUpdate;	
	}

	/**
	 * Start observing changes in your realtime database.
	 */
	Firebase.prototype.start = function() {
		this._isObserving = true;
		fetch.call(this);
	}

	/**
	 * Stop observing changes in your realtime database.
	 */
	Firebase.prototype.stop = function() {
		this._isObserving = false;
	}

	/**
	 * Get a description for debugging purposes.
	 * 
	 * @return {String}
	 */
	Firebase.prototype.toString = function() {
	  return 'Firebase("' + this._url + '")';
	}

	// -- Private

	/**
	 * Fetch realtime database once.
	 */
	function fetch() {
		const self = this;

		N.fetch(self._url).then(function(result) {
			if (self._isObserving) {
				fetch.call(self);
			}

	  	if ((result.status >= 200) && (result.status < 300)) {
	  	  return result.json();
	  	}

	  	throw new Error("HTTP status code " + result.status);
		}).then(function(json) {
			if (self._onUpdate != null) {
				self._onUpdate(json);
			}
		}).catch(function(error) {
	 		D.log("There was an issue with fetch operation: " + error.message);
		});
	}

	// -- Export

  return Firebase;
})();

// -- Modules

const S = require("Scene");
const TG = require("TouchGestures");

// -- Constants

const URL = "YOUR OWN FIREBASE ADDRESS i.e) https://YOURPROJECTNAME.firebaseio.com/.json";

// -- Scene

const counterText = S.root.find("Counter Text");
const decrementButton = S.root.find("Decrement Button");
const incrementButton = S.root.find("Increment Button");

// -- Example

var data = null;

var firebase = new Firebase(URL);
firebase.subscribe(function(e) {
	data = e;
	counterText.text = `${data.counter}`;
});
firebase.start();

TG.onTap(decrementButton).subscribe(function(e) {
	data.counter = data.counter - 1;
	firebase.set(data);
});

TG.onTap(incrementButton).subscribe(function(e) {
	data.counter = data.counter + 1;
	firebase.set(data);
});