Building a Countdown Timer with Socket.io

Yesterday I put together a very simple Node/Socket.io application and showed how to deploy it to Heroku. Today I'm going to keep going with that app to see if I can get the functionality that I want. The app is a basic stopwatch so that shouldn't be too hard. If you want to catch up checkout yesterday's article which explains setting everything up.

Countdown

Just to get the ball rolling I'm going to write a little code in my app.js file right at the bottom to setup a very crude counter.

var countdown = 1000;  
setInterval(function() {  
  countdown--;
  io.sockets.emit('timer', { countdown: countdown });
}, 1000);

io.sockets.on('connection', function (socket) {  
  socket.on('reset', function (data) {
    countdown = 1000;
    io.sockets.emit('timer', { countdown: countdown });
  });
});

Elsewhere in my client-side js I'm going to listen for the timer event and update my DOM elements.

var socket = io.connect(window.location.hostname);

socket.on('timer', function (data) {  
    $('#counter').html(data.countdown);
});

$('#reset').click(function() {
    socket.emit('reset');
});

You'll also need to update your index.ejs file so it reads like this:

<div id="counter"></div>  
<button id="reset">Reset!</button>  

Every second we'll decrement our countdown variable and broadcast its new value. If a client sends us a reset event we'll restart the timer and immediately broadcast the update to anyone connected. I noticed that since I'm using xhr-polling it can sometimes take a while for the timer to show up in my browser so keep that in mind.

While this implementation isn't pretty it does get us a little bit further down the road. Unfortunately I've been tripped up by a bunch of Node's module issues so I have to cut tonight's post short :\

Hopefully better luck tomorrow. - Rob

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