Question

I just got my first app up and running on Node.js. As of now, it is simply serving up a static file. But I have a few ideas that will be implemented down the road so I’m going ahead and getting Node setup so I’ll be ready for it when that time comes.

// get modules
var express = require('express');
var fs = require('fs');

// create app instance
var app = express();

// static files middleware
app.use("/assets", express.static(__dirname + '/assets'));

// main route
app.get('/', function(req, res) {
    var html = fs.readFileSync('assets/views/main.html', 'utf8');
    res.send(html);
});

// make web server listen on specific port
app.listen(8080);

NOTE: I realize I don’t need Express to serve one route, but I figured what’s the harm in getting a head start on that as well?! 🙂

The first idea i had is to make a way to let all users currently using the app that there has been an update and that they must refresh their browser. There is no need to save the current state of the app as it is pretty basic.

So, if I am a user, I’m using the app and boom, I get a pretty little modal-window-alert-notification thingy letting me know that I need to refresh.

Also, if some user loads the app AFTER I have sent the alert, that user should not see the alert at all (because they should already be seeing the new changes).

I have done some googling on the subject and I’m just not satisfied with the examples i found. I do not think I want to have to update a notifications.xml file (which node.js would be watching) to push a new notification.

One solution I can think of would be to make a command that can be executed from the command line that will (somehow) send a new notification to the app. Perhaps using something like Grunt.js (I’m not sure if it would be a good fit for this as I’ve never used it). Basically, once the notification has been sent, all traces of it should disappear. That’s why I think a command line approach would be good.

Here’s my question: How (generally speaking) should I implement something like this? I am a Node.js newbie but I am pretty comfortable with javascript and the command line.

Please feel free to offer up any alternative solution you think would be better for me (other than a command line approach), or any tools that you think could help me.

Thanks!

Answer 1

If you want to push updates to a web client, one way is to use something like Socket.io. This creates a two-way pipe between client and server that you can use to asynchronously push updates through.

Sample server:

var app = require('express').createServer()
  , io = require('socket.io').listen(app);

app.listen(80);

app.get('/', function (req, res) {
  res.sendfile(__dirname + '/index.html');
});

io.sockets.on('connection', function (socket) {
  socket.emit('news', { hello: 'world' });
  socket.on('my other event', function (data) {
    console.log(data);
  });
});

Sample client:

<script src="/socket.io/socket.io.js"></script>
<script>
  var socket = io.connect('http://localhost');
  socket.on('news', function (data) {
    alert('New news has come in! Please refresh your page!');
    socket.emit('my other event', { my: 'data' });
  });
</script>

The other option is to poll from the client using Javascript to actively look for updates. You would need to keep some state on the server for each client that would determine if that client required an update. The client would then make a get request on some timer interval (once a second, for example) to a secondary route and the server would reply with ‘Yes, you need an update’ or ‘No, you don’t need an update’. If yes, the client Javascript would then pop up your modal box and tell the user to refresh.