Hi Everybody,

I feel sorry to inform you that I could not continue my this blog account because of some technical and personal difficulties. Currently I am trying to actively update, post and share my novice knowledge in the following link

URL: http://novicearshad.wordpress.com
Title: A Novice Software Engineer’s Diary

Thanks for being connected…

Md. Arshad Hossain

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JavaScript Snippets

April 12, 2011

// inArray() as like as PHP inArray function
function inArray(needle, theArr){
for(var i=0; i<theArr.length; i++){
if(theArr[i] == needle){
return true;
}
}
return false;
}

Now-a-days, this is a very common question that been asked in all most every basic interview – What is the main strength of AJAX? Or why and when should we use AJAX in web application?
And the most common answer is – “AJAX does not refresh or reload the whole page”.

But, the more perfect answer is – “AJAX is an asynchronous technology where others request are synchronous.”

So, what is the difference?

In a word, a program does not wait for response after requesting an asynchronous call whereas synchronous does so.

Here is a simple example –

function check() {
var a=0;
a = getStatus(“getstatus.php?id=5”);
if(a==1) {
alert(“active”);
} else {
alert(“not active”);
}
}

Here getStatus() function sends a AJAX request to the server with “getstatus.php?id=5” url and the php file decides (from database may be) the status and output/response as 1 or 0.

But, this function will not work properly. It will alert “not active” instead of “active”. And yes, that is for the asynchronous request.

The reason is – when a = getStatus(“getstatus.php?id=5”); line is being executed program does not wait for the response of setStatus() function. So, value of keep unchanged or set to null.

So, how should we work with asynchronous request?

Of course, using callback function. Callback function is that function which is triggered when the request completes to get the response (or as defined).

Session is the most widely used PHP feature which is being used for security purpose. From beginner to expert, almost all coder feel comfort using session as for its wonderful feature (preserving data across subsequent accesses) .
But question is, where actually session data be saved? In client browser URL or in browser cookie? Or, in server?

First and simple answer is – session born in server and uses browser’s cookie to keep track (alive) by an Id. If cookie is not enabled, it parses to browser URL as variable (serialized).

Now, how can server remember the huge number of variables that is registered with session? Specially when PHP is installed as CGI wrapper, as PHP interpreter is created and destroyed for every page request.

Yes, server needs to save those data in its physical memory too.
Session creates a file to save its information at the location assigned by session_save_path() function or set by session.save_path option.

So, at the final sentence, we can say that session uses  memory – server side (physical file in session_save_path location) to save all data and client side (physical file cookie) or in URL as a variable where just a unique ID (sesssion id) is saved.

Today my colleague, Al-Amin Rubel, faces a interesting (but very common of course) problem –

“Pages are not being reloaded/ refreshed after contents are updated by AJAX” that means AJAX request always returns/responses same data from server although data has already been changed. But, more interesting matter is in mozilla FIREFOX is working fine whereas I.E (internet explorer) showing same output.

After debugging a lot, it was clear that whenever request URL of ajax is exactly same as previous request, it loads the output from cache.

Solution:

So, perhaps the best solutions is to change the url every time. Don’t afraid, this is very simple, just add a url variable with random value using random() function.

Example:

Suppose, your AJAX request URL is – “ajaxresponse.php?name=xyz&res=123”

Then change it by adding a variable with random value – like

‘ajaxresponse.php?name=xyz&res=123&rnd=’+Math.random(10);

That’s it, solved!

This is because browser takes the url as a new request (url) every time.