Friday, January 17, 2014

Experimenting with Node.js

Node.js seems particularly suited for small real-time web pages where users can see event-driven data be updated on the webpage without a page refresh.  I spent a couple hours this weekend learning about node.js so I made a simple long polling web server based on one of the examples from this article.

To get my Ubuntu VM ready to do this, I did the following:
-downloaded the node-v0.10.24-linux-x64.tar.gz and untarred the package.  I had all the prereqs from the file, except python
-installed python 2.7.2.  Since I hadn't used python scripting before, decided to dabble a bit in that by writing a few statements in a python script to get used to python syntax

The Simple Long Polling Web Server Example:
The node.js web server is polling every 10000 milliseconds, and if the current time in milliseconds modulus 3 is zero, then it returns the time to the caller.  A simple html webpage is making an ajax call to the node.js web server, and will append the time if conditions are satisfied.  Here's the output of it:


  1. server_longpoll.js:
    var sys = require('sys'),
       http = require('http');
    http.createServer(function(request, response) {
      getTime(request, response);
    function getTime(request, response)
      var now = new Date();
      var timeInMilliseconds = now.getTime();
      // event that is listening is: if time is modular by 3
      if ((timeInMilliseconds % 3) == 0)
        // return the contents
        response.writeHead(200, {
          'Content-Type'   : 'text/plain',
          'Access-Control-Allow-Origin' : '*'
        // return response
        // return
        return false;
      setTimeout(function() {getTime(request, response) }, 10000);
  2. cherryshoe_longpoll.html:
    <meta charset="UTF-8">
    <title>Sample ajax call to node server with long polling</title>
    Polling every 10000 milliseconds... </br>
    Current time in milliseconds where modulus 3 is zero: <div id="updateId"></div>
    <script src="jquery-1.9.1.js"></script>
    <script src="cherryshoe_longpoll.js"></script>
  3. cherryshoe_longpoll.js:
    $(document).ready(function() {
            function callNodeJs() {
                            // setup the server address
                            url : 'http://judyhost:8000',
                            success : function(response, code, xhr) {
                                // on success
                                $('#updateId').append(response + "</br>");
                            error : function() {
                              // on error
This example is obviously very simple, but can easily be modified to watch for ANY event to happen and solved in the same fashion.


  1. Thanks for this post Judy. I'm just getting into Node.js myself so this gives me great info to learn from.

    Jeff Hendrickson


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