Cherry Shoe Technologies: 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 README.md 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:

Files:

server_longpoll.js:

var sys = require('sys'),
   http = require('http');

http.createServer(function(request, response) {
  getTime(request, response);
}).listen(8000);

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
    response.write(timeInMilliseconds.toString());
    response.end();

    // return
    return false;
  }

  setTimeout(function() {getTime(request, response) }, 10000);

};

cherryshoe_longpoll.html:

<head>
<meta charset="UTF-8">
<title>Sample ajax call to node server with long polling</title>
</head>

<body>
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>
</body>
</html>

cherryshoe_longpoll.js:

$(document).ready(function() {
        function callNodeJs() {
                $.ajax({
                        // setup the server address
                        url : 'http://judyhost:8000',
                        success : function(response, code, xhr) {
                            // on success
                            $('#updateId').append(response + "</br>");
                                callNodeJs();
                        },
                        error : function() {
                          // on error
                          alert("error");
                        }
                });
        };

        callNodeJs();
});

This example is obviously very simple, but can easily be modified to watch for ANY event to happen and solved in the same fashion.

Friday, January 17, 2014

Experimenting with Node.js

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