Why does my server shut down after a websocket closes?

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Javascript

Node.js

WebSockets

, +

My node.js server randomly shuts down after a client has connected from a web and then closes the tab (simple disconnection).

The server:

var websocketServer = require("ws").Server, 
    server = new websocketServer({port: 9000});

var date = require("./modules/date");

console.log("[" + date.timestamp() + "] creating the websocket server..");

server.on("connection", function(websocket) {
	console.log("[" + date.timestamp() + "] receiving a connection from " + websocket._socket.remoteAddress);

    websocket.on("message", function(message) {
        console.log("received: %s", message); 
        websocket.send(message);
    });
    websocket.send("something");
});

console.log("[" + date.timestamp() + "] server is open for connections on port 9000");

Client:

var socket;

$(document).ready(function() {
	socket = new WebSocket("ws://127.0.0.1:9000");

	socket.onopen = function(){
		if(stage == "5fb26f935a4358dce53e6ce67a08c1b5e73dc7f8c554615ae33ac1d6ecb214b6") {
			stage = "27e1c570b1f1e08cb35019c63f3830828ce18f70fa95eecfcfa84f1e019c3929";
			$("section.loader").animate({"top": "-100%"}, 1000);
		}
	};

	socket.onmessage = function(e) {
		alert("recieved: " + e.data);
	};

	socket.onerror = function(e) {
		if(stage == "5fb26f935a4358dce53e6ce67a08c1b5e73dc7f8c554615ae33ac1d6ecb214b6") {
			$("body").append("<div class='error'>\
					Something went wrong!<br>The server could not respond to your request, please try again in a bit.\
				</div>");
			$("body div.error").animate({"bottom": "0px"}, 500);

			setTimeout(function(){
				$("body div.error").animate({"bottom": "-58px"}, 500, function() {
					location.reload();
				});
			}, 5000);
		}
	};

	socket.onclose = function() {
	};
});

What I have tried:

I'm fairly new to node.js and I don't know what else to really try to edit since I can't see any malfunction code by my eye.