WebEvents/client.js

(function() {
	function post(url, cb) {
		let cbd = false;
		function c(err, res) {
			if (cbd) return;
			cbd = true;
			cb(err, res);
		}

		setTimeout(() => c("ETIMEDOUT"), 5000);

		fetch(url, { method: "POST" })
			.then(response => response.json())
			.then(obj => {
				if (obj.error)
					c(obj.error);
				else
					c(null, obj);
			})
			.catch(err => {
				c(err);
			});
	}

	window.WebEvents = function() {
		var self = {};

		var cbs = {};
		var key = null;

		function emit(name, args) {
			if (!cbs[name])
				return;

			cbs[name].forEach(function(cb) {
				cb(args);
			});
		}

		function init() {
			console.log("init...");
			post("/webevents/register", function(err, res) {
				console.log("Init done,", err ? "with errors" : "no errors");

				// Retry on error
				if (err) {
					console.log(err);
					setTimeout(function() { init() }, 2000);
					return;
				}

				emit("connection");
				key = res.key;
				await();
			});
		}

		function await() {
			post("/webevents/await/"+key, function(err, res) {
				// Retry on error
				if (err === "ENOTREGISTERED") {
					console.log("Not registered, reregistering");
					setTimeout(init, 2000);
					return;
				} else if (err == "ETIMEDOUT") {
					console.log("Timed out.");
					setTimeout(await, 0);
					return;
				} else if (err) {
					console.error("Error:", err.toString());
					emit("$error", err);
					setTimeout(init, 2000);
					return;
				}

				res.forEach(function(evt) {
					emit(evt.name, evt.args);
				});

				await();
			});
		}

		self.on = function(name, cb) {
			if (!cbs[name])
				cbs[name] = [];

			cbs[name].push(cb);
		};

		init();

		return self;
	}
})();