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Syncing Events between 2 JS apps

I have a game app (Electron) and a web app (testing on android chrome). That pass messages via a websocket server. I want to coordinate a countdown between the 2 processes. It doesn't have to be perfect but What I've observed is that if I run in an environment with low latency it's fine. But the more lag their is in the system it seems like the Electron app tries to start far earlier then the web app. I've tested all my math and it should synchronize but it just doesn't.
First the web app iniates the start of the countdown by passing a starting time to the game app
const timeToGameStart:number = peerConnection.timeToGameStart(); // time to game start = 3 x (the longest time it toke to pass a previous msg from game app to web app)
const currUnixTime:number = peerConnection.currUnixTime();
const startGameTime:number = currUnixTime + timeToGameStart;
const startGame:StartGame = <StartGame>{
msg_data_type:Msg_Data_Type.StartGame,
game_start_time:startGameTime
}
peerConnection.passMsg(startGame);
setTimeout(timer.start, timeToGameStart);
Below is the app portion of the code that responds to the msg passed to the server
const gameStartTime:number = (<StartGame> msgData).game_start_time;
const currUnixTime:number = ServerConnection.currUnixTime();
// if we are on time, wait till its right time else if we are late, start at the next inc 3,2,1
const countDownLength:number = 3;
if (currUnixTime <= gameStartTime) {
setTimeout(()=>startCountDown(countDownLength), currUnixTime - gameStartTime);
} else {
const timeWeAreLateBy:number = currUnixTime - gameStartTime;
const timeWeAreLateByInSec:number = Math.ceil(timeWeAreLateBy / 1000);
const shortCountDownLen:number = Math.max(countDownLength - timeWeAreLateByInSec, 0);
const timeToNextSec:number = Math.max((1000 * timeWeAreLateByInSec) - timeWeAreLateBy, 0);
setTimeout(()=>startCountDown(shortCountDownLen), timeToNextSec);
}

The problem is that these two separate processes are on separate OSs. Which both have a different definition of time. i.e. (new Date()).getTime() return different numbers. the difference was 2 seconds so the controller thought their was no lag in the connection and was telling the app to start ASAP.
The solution was I had to define a consistent measurement of time. After each app connects to the server they sync their time with the server by making a request for the time the server has.
I didn't need a super precise time sync so I used a simple algorithm that got the job done. The algorithm was trying to calculate the difference in time the process was off from the server. The formula I used was server_time_diff = server_time - (received_time - RTT/2). Now to get unified (or server time) you just need to call new Date() + server_time_diff. RTT is the time it took to request the time from the server.
Any improvement ideas to my algorithm is welcome.

JavaScript loop ranges and code execution (port scanner)

I'm having an issue with calling a function in a loop, with JavaScript. As I'm new to JavaScript, I thought perhaps my approach must be wrong. Can someone help me out with the following issue?
Basically, each time I learn a new language, I try and write a port scanner in it. In Python, I used a for loop to iterate over a range of numbers, passing them in as ports to a host. It worked fine and I attempted the same approach in JavaScript, with some socket connection code I found online:
const net = require('net');
function Scanner(host, port){
const s = new net.Socket();
s.setTimeout(2000, function() { s.destroy(); });
s.connect(port, host, function () {
console.log('Open: '+ port);
});
s.on('data', function(data){
console.log(port +': ' +data);
s.destroy();
});
s.on('error', function (e) {
s.destroy();
})
}
for(let p = 15000; p < 30000; p++){
let scan = new Scanner('localhost', p);
}
In the above example, I'm iterating over a port range of 15000 to 30000. It appears to run very fast, giving me two results: port 15292 and 15393 as being open on my test vm. However, it's not picking up several ports in the 20,000 range, like 27017.
If I narrow the range from 25000 to 30000 it picks those up just fine. The problem seems to be when I have a larger range, the code isn't discovering anything after a few hits.
In looking at some other JS implementations of port scanners, I noticed the same issue. It works great when the range is 5,000 ports or so, but scale it up to 20k or 30k ports and it only finds the first few open ones.
What am I doing wrong?

Slow performance on Mac OS X

I am currently learning how to use NightmareJS. I found the performance is so slow while I was running the code below. It took up to 30 seconds to get the output. Did I do anything wrong?
Moreover, I have tried to use wait() with a selector but that does not help so much.
I am not sure whether this is related to my Internet connection, however, open the same site using Google Chrome and perform the same task is faster than using Nightmare.
Soruce Code
var Nightmare = require('nightmare');
var after;
var before = Date.now();
new Nightmare({
loadImages: false
}).goto('https://www.wikipedia.org/')
.type('#searchInput', process.argv[2])
.click('input[name="go"]')
.wait()
.url(function(url) {
after = Date.now();
console.log('>>> [' + (after - before) / 1000.0 + 's] ' + url);
})
.run(function(err, nightmare) {
if (err) console.log(err);
});
Output
node n02_extract_wiki_link.js "node.js"
>>> [31.227s] https://en.wikipedia.org/wiki/Node.js
My current environment is listed below.
Mac OS X 10.10.4
node v0.12.5
PhantomJS 2.0.0
nightmare#1.8.2

This worked for me:
https://github.com/segmentio/nightmare/issues/126#issuecomment-75944613
It's the socket connection between the phantomjs module and it's dependency, shoe.
You can manually edit shoe yourself. Go into node_modules/phantom/shoe/index.js and change line 8 to read
var server = sockjs.createServer({
heartbeat_delay : 200
});

node-serialport on windows with multiple devices hangs

I've been experimenting with node-serialport library to access devices connected to a USB hub and send/receive data to these devices. The code works fine on linux but on windows(windows 8.1 and windows 7) I get some odd behaviour. It doesn't seem to work for more than 2 devices, it just hangs when writing to the port. The callback for write method never gets called. I'm not sure how to go about debugging this issue. I'm not a windows person, if someone can give me some directions it would be great.
Below is the code I'm currently using to test.
/*
Sample code to debug node-serialport library on windows
*/
//var SerialPort = require("./build/Debug/serialport");
var s = require("./serialport-logger");
var parsers = require('./parsers');
var ee = require('events');
s.list(function(err, ports) {
console.log("Number of ports available: " + ports.length);
ports.forEach(function(port) {
var cName = port.comName,
sp;
//console.log(cName);
sp = new s.SerialPort(cName, {
parser: s.parsers.readline("\r\n")
}, false);
// sp.once('data', function(data) {
// if (data) {
// console.log("Retrieved data " + data);
// //console.log(data);
// }
// });
//console.log("Is port open " + sp.isOpen());
if(!sp.isOpen()) {
sp.open(function(err) {
if(err) {
console.log("Port cannot be opened manually");
} else {
console.log("Port is open " + cName);
sp.write("LED=2\r\n", function(err) {
if (err) {
console.log("Cannot write to port");
console.error(err);
} else {
console.log("Written to port " + cName);
}
});
}
});
}
//sp.close();
});
});
I'm sure you'd have noticed I'm not require'ing serialport library instead I'm using serialport-logger library it's just a way to use the serialport addons which are compiled with debug switch on windows box.

TLDR; For me it works by increasing the threadpool size for libuv.
$ UV_THREADPOOL_SIZE=20 && node server.js
I was fine with opening/closing port for each command for a while but a feature request I'm working on now needs to keep the port open and reuse the connection to run the commands. So I had to find an answer for this issue.
The number of devices I could support by opening a connection and holding on to it is 3. The issue happens to be the default threadpool size of 4. I already have another background worker occupying 1 thread so I have only 3 threads left. The EIO_WatchPort function in node-serialport runs as a background worker which results in blocking a thread. So when I use more than 3 devices the "open" method call is waiting in the queue to be pushed to the background worker but since they are all busy it blocks node. Then any subsequent requests cannot be handled by node. Finally increasing the thread pool size did the trick, it's working fine now. It might help someone. Also this thread definitely helped me.

As opensourcegeek pointed all u need to do is to set UV_THREADPOOL_SIZE variable above default 4 threads.
I had problems at my project with node.js and modbus-rtu or modbus-serial library when I tried to query more tan 3 RS-485 devices on USB ports. 3 devices, no problem, 4th or more and permanent timeouts. Those devices responded in 600 ms interval each, but when pool was busy they never get response back.
So on Windows simply put in your node.js environment command line:
set UV_THREADPOOL_SIZE=8
or whatever u like till 128. I had 6 USB ports queried so I used 8.

<video>.currentTIme doesn't want to be set

I'm trying to write a piece of Javascript that switches between two videos at timed intervals (don't ask). To make matters worse, each video has to start at specific place (about ten seconds, and again, don't ask.)
I got the basics working by just using the YUI Async library to fire to switch the videos at intervals:
YUI().use('async-queue', function (Y) {
// AsyncQueue is available and ready for use.
var cumulativeTime = 0;
var q = new Y.AsyncQueue()
for (var x = 0; x < settings.length; x++) {
cumulativeTime = cumulativeTime + (settings[x].step * 1000)
q.add( {
fn: runVideo,
args: settings[x].mainWindow,
timeout: cumulativeTime
})
}
q.run()
});
So far, so good. The problem is that I can't seem to get the video to start at ten seconds in.
I'm using this code to do it:
function runVideo(videoToPlay) {
console.log('We are going to play -> ' + videoToPlay)
var video = document.getElementById('mainWindow')
video.src = '/video?id=' + videoToPlay
video.addEventListener('loadedmetadata', function() {
this.currentTime = 10 // <-- Offending line!
this.play();
})
}
The problem is that this.currentTime refuses to hold any value I set it to. I'm running it through Chrome (the file is served from Google Storage behind a Google App Engine Instance) and when the debugger goes past the line, the value is always zero.
Is there some trick I'm missing in order to set this value?
Thanks in advance.

Try use Apache server.
setCurrentTime not working with some simple server.
ex) python built in server, php built in server
HTTP server should be Support partial content response. (HTTP Status 206)