When you want to null the sliders on an page, using jQuery UI Slider, somehow the following code works in any browser except IE.

// wrong
$('.my-slider').slider('value', 0);

I say somehow, because according to the documentation this code is simply wrong. It can be used to get the value of the slider as it is a getter. You can null the value with the following snippet.

// correct
$('.my-slider').slider('option', 'value', 0);

IE Fix

Another way to null the value is with an anonymous object.

// correct
$('.my-slider').slider({ value: 0 });

This works on every browser including IE.

Typically in jQuery when you bind an HTML element with some event this event is fired every time the user (client) triggers it. Thus when you’ve a click event attached on a button you can click it as many times as you want. In some rare cases this can be tricky. Let’s imagine the following scenario.

1. The user clicks on a “vote” button.
2. Some AJAX calls are performed.
3. After a successful AJAX call you setup a cookie to deny further votes from this machine.

This seems to be pretty well known scenario, but as the click event is attached to the button there is enough time to click several times on the “vote” button and to vote several times. In this case before the cookie is set the user can vote more than once.

Demo

So one possible solution is to unbind the click event. In jQuery terms this is done by …

$.unbind()

With this method you can simply unbind the “click” event or whatever event there is attached on the desired HTML element. So now in the first case we had:

$(document).ready(function() {
    $('input').click(function() {
        $.ajax({ url : 'http://stoimen.com/projects/jquery.unbind/example1.php'
               , success : function() {
                    $('p').append('You\'ve voted successfully!
');
               }    
        }); 
    }); 
});

Now you can replace the code above with:

$(document).ready(function() {
    $('input').click(function() {
        $('input').unbind();
        $.ajax({ url : 'http://stoimen.com/projects/jquery.unbind/example1.php'
               , success : function() {
                    $('p').append('You\'ve voted successfully!
');
               }    
        }); 
    }); 
});

As you can see on the demo here now the button cannot be clicked more than once.

Demo

Cookies + unbind()

There is a problem however. After reloading the page the event is attached again, so the user can click on the button once more. The obvious solution is to combine both the cookie and the unbind() as shown in the following pseudo code.

$(document).ready(function() {
    if (cookie is not set) { 
        $('input').click(function() {
            $('input').unbind();
            $.ajax({ url : 'http://stoimen.com/projects/jquery.unbind/example1.php'
                   , success : function() {
                        $('p').append('You\'ve voted successfully!
');
                        set cookie
                   }    
            }); 
        });
    } 
});

What is typical for most of the web servers is that they listen for requests and respond as quickly as possible on every one of them. In fact the speed of the response is one of the main targets of optimization for developers. Fast servers are what everyone needs. From web developers to website visitors!

In the field of the that battle different web servers have different “weapons” to gain time. While this is useful in most of the cases, when it comes to a chat-like applications and Node.js approaches, the response is not always immediately returned. As I described in my posts until now about Node.js, a simple web server may wait for an event to be emitted, and than return the response.

I wrote about how to write the very first server, but than I didn’t described how to make a “non-responding” server. By the term “non-responding” I mean a server that responds not immediately after it has received and parsed/executed the request.

A typical web server, responding immediately on every request, written with Node, this may look like so:

var http = require('http');
http.createServer(function (req, res) {
  res.writeHead(200, {'Content-Type': 'text/plain'});
  res.end('Hello World\n');
}).listen(8124, "127.0.0.1");
console.log('Server running at http://127.0.0.1:8124/');

The code that shows us that the request is executed and responds in these lines:

  res.writeHead(200, {'Content-Type': 'text/plain'});
  res.end('Hello World\n');

Actually by commenting/removing those lines you’ll get a server that simply doesn’t respond – ever! This of course is not the main goal, but you can start from somewhere.

var http = require('http');
http.createServer(function (req, res) {
  // res.writeHead(200, {'Content-Type': 'text/plain'});
  // res.end('Hello World\n');
}).listen(8124, "127.0.0.1");
console.log('Server running at http://127.0.0.1:8124/');

This is how you can hold for a while. Perhaps putting these lines in a conditional statement and periodically checking for some event to occur will do the job.

var http = require('http');
http.createServer(function (req, res) {
  if (something) {
     res.writeHead(200, {'Content-Type': 'text/plain'});
     res.end('Hello World\n');
  }
}).listen(8124, "127.0.0.1");
console.log('Server running at http://127.0.0.1:8124/');

Looping Server

As described in the code above if you put the respond into a conditional you can possibly return the response after some event has fired. The only thing is to periodically loop and check for this condition to be true. Assuming your server’s code is in server.js, started with the “node server.js” command, you’ve to put this code into it:

var http = require("http"),
    fs	 = require("fs");  

// we create a server with automatically binding
// to a server request listener
http.createServer(function(request, response) {
	checkFile(request, response);
}).listen(8124);

function checkFile(request, response)
{
	var date = new Date();
	if (date-request.socket._idleStart.getTime() > 59999) {
		response.writeHead(200, {
			'Content-Type'   : 'text/plain',
			'Access-Control-Allow-Origin' : '*'
		});

		// return response
		response.write('OK', 'utf8');
		response.end();
	}

	// we check the information from the file, especially
	// to know when it was changed for the last time
	fs.stat('filepath', function(err, stats) {
		// if the file is changed
		if (stats.mtime.getTime() > request.socket._idleStart.getTime()) {
			// read it
			fs.readFile('filepath', 'utf8', function(err, data) {
				// return the contents
				response.writeHead(200, {
					'Content-Type'   : 'text/plain',
					'Access-Control-Allow-Origin' : '*'
				});

				// return response
				response.write(data, 'utf8');
				response.end();

				// return
				return false;
			});
		}
	});	

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

Note: you must change “filepath” with an existing file path in your system.

Here we can read periodically the file’s mtime, which is the modify time. Thus whenever the file is changed the server will return the response. It’s interesting to note that if no change occurs within the timeout period you’ve to return some status message as we did in those lines:

        
var date = new Date();
if (date-request.socket._idleStart.getTime() > 59999) {
	response.writeHead(200, {
		'Content-Type'   : 'text/plain',
		'Access-Control-Allow-Origin' : '*'
	});
	
	// return response
	response.write('OK', 'utf8');
	response.end();
}

The client side should long poll this server. The example bellow is written in jQuery. The only “special” thing is that after receiving the response, you must call the server again.

The Client

The client is nothing new to the jQuery/JavaScript community except you must call again the server when the response is returned:

function callNode() {
    $.ajax({
        cache : false,
		// setup the server address
        url : 'http://www.example.com:8124/',
        data : {},
        success : function(response, code, xhr) {

            if ('OK' == response) {
            	callNode();
                return false;
            }

            // do whatever you want with the response
            ...

            // make new call
            callNode();
        }
    });
};
callNode();

Summary

As Node can hold the response, the only thing you should do is to check periodically for something as in this example this was a file change. Than it’s important to change the client so it can call the server after the response from it is received.

Typically Node can be used for chat-like applications or whatever apps that must deliver real time data, but for sure it is really great software.

$('path').attr('fill', '#ccc');

If you’re familiar with jQuery you should already know what are selectors and how they work. However we’re used to get some DOM element with a specific selector, but actually sometimes you cannot select directly what you need. This is especially true when mixing more than one JavaScript libraries. In my case OpenLayers generated a vector layer and jQuery was supposed to change the vectors fill-color property.

With the simple $(‘path’) I easily got all vectors in the current document, but the problem was that I took them as text. Thus it came to me to use nested jQuery – $($(‘selector’));

To describe what actually happened in my case, let me show you a breve example.

Example

Here’s a short HTML markup:

text text

With jQuery I can select both the DIV and SPAN with the simple $(‘div’) and $(‘span’), but just for the example lets assume I’ve only the inner text of the DIV tag:

$('div').html();

That was the case in the OpenLayers/jQuery problem. Now I can easily use another jQuery selector:

$($('div').html());

This will return the same as $(‘span’) – a jQuery object.

Animation

As I said animating some vector properties is as simple as:

var paper = Raphael('canvas', 1024, 500);
var c = paper.circle(50, 50, 6).attr({fill : '#f00'});
c.animate({r : 10, fill : '#00f'}, 1000);

Here we change the radius and the background color of the circle for 1000 milliseconds.

The same thing can be done with any property with any other JavaScript library as jQuery. But as in jQuery, Raphael or whatever library the animation is not looping. That’s natural you can just change a property by animating it, but the looping animation suggests at least two animations. So it’s a developers job to implement this. Here’s a simple way to do this.

Two Way Animation

The solution here is using two functions calling each other.

var paper = Raphael('canvas', 1024, 500);
var c = paper.circle(50, 50, 6).attr({fill : '#f00'});

function a() {
    c.animate({r : 10, fill : '#00f'}, 1000, b);
}
function b() {
    c.animate({r : 6, fill : '#f00'}, 1000, a);
}
a();

First of all let me explain what is the task. If there’s a select menu with several options, each of which are with a given value attribute, the task is to get the text into the option tag, and not that of the value attribute.

In that scenario let’s assume that we have the following HTML:

    value 1
    value 2

Note that in the official jQuery doc page, the selector is described in the same context, but with a different markup:

    value 1
    value 2

than the jQuery snippet looks like that:

$(document).ready(function() {
    $("#my-select").change(function() {
        alert($(this).val());
    });
});

Here’s interesting to note that there’s no value attribute set to the options, thus the selection of an element is correct and the returned value is correct. The problem is that this code doesn’t work correctly once you’ve a different value attribute, from the value enclosed into the option tag. In our case we’ve the markup shown on the first code snippet and we’d like to get the “value 2” string instead of “2”.

Source Code

    value 1
    value 2

$(document).ready(function() {
    $("#my-select").change(function() {
        alert($(this).val());
    });
});

Solution

Finally the solution, is pretty simple and clear, but this time is not to so “native” and it’s definitely something you couldn’t expect! The only thing you’ve to do is to change the selector!

$(document).ready(function() {
    $("#my-select).change(function() {
        alert($('#my-select option:selected').html());
    });
});

Here’s a short optimization of a small chunk of jQuery code. The experiment was to increment the number of DOM element access. In this case this was a change of the innerHTML property – using the $.html() method.

I’ve measured the result with the console.time() method and thus I expect correct results for both cases. In the first case I directly call the jQuery selectors’ html() method:

for (var i = 0; i < 10000; i++) {
    $('#container').html(i);
}

While in the second case I "cache" it before the loop:

var t = $('#container');
for (var i = 0; i < 10000; i++) {
    t.html(i);
}

and here's the full code in the first case:

The Results

As expected the second "cached" approach gave better results. With the increment of the iterations the second method began to be slightly better than the first one. That's not so much, but imagine you have more than one selector in the loop's body?

Numbers:

Note that in the time is in ms, and, yes, this is not so much, but when you deal with large data and you've more than one selector in the loop's body, this can be critical!

Graphics:

Here’s the HTML:

    
Node 1
    
Node 2
    
Node 3
    
Node 4

And that’s the jQuery:

var index = 5;
$('li > a').live('click', function() {
    $(this).parent().append('
Node ' + index + '
');

    index++;

    return false;
});

And here’s the demo.

The job can be done with a event’s which check. Let me show you some JavaScript/jQuery code:

$('.selector').click(function(e) {
	console.log(e.which);	
});

Note that this can be checked under Firefox and/or Safari like browsers which support the console object. This will give you the idea which key is pressed in a number value. The Enter is usually 13!
If you don’t have such browser, you can replace that code with something like:

$('.selector').click(function(e) {
	alert(e.which);	
});