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Is it possible to get data from redirection page in AJAX?

I'm in trouble. I'm trying to do something which can appear easy but I don't manage to do it.
Here is the situation :
I have 3 different html pages :
The first one called index.html is my main page with a button to lauch a test in AJAX (I'm gonna talk about it after).
The second one corresponds to a redirection to the third page.
The third one has data.
What I wanna do is :
Click on "test" button on the first page and then start an AJAX request on the second one to reach data from the third one (with the redirection) to print it in the first.
I mean the first page calls the second one in AJAX, but the just to redirect on a specific third page. Depending on the third page which is called, data returned to the first page will change.
Do you think it's possible to find a solution to this problem in Javascript ? I hope I have been clear enough.
Thank you in advance for answer.

What you are describing doesn't really make sense. There are methods of redirection that AJAX follows (an HTTP 301 code, for example). However, what you are describing is not that sort of redirect. You are describing Javascript code that, when run, will redirect the browser elsewhere.
However, you are not loading that Javascript with the browser, you are downloading the page via AJAX. Once it is downloaded, you will have the text that represents that page, but in order to find out where it would redirect to when run, you would either have to run it and somehow capture the redirect value (not recommended), or parse it yourself (also not recommended).
There are other options that could work, depending on what you are trying to accomplish:
The server could return an HTTP redirect code when the second page is requested
The second page could instead be a text or JSON file containing a URL, which the first page could read, then request data from that URL.
If there is logic in the second page that determines where the redirect goes, it could be moved to the first page
You could have the second page employ server-side scripting (PHP, etc) to determine what data should be returned and return it directly to the first page

What is the right way to call dynamic content (currently using ajax) inside a cached page?

We have a news website where we cache a complete article page.
There are 4 areas that need to continue to be dynamic on that page:
View Counter: We add +1 to view_counts of that article when page loads.
Header: On the header of the website we check if session->id exists or not if it does we display a Welcome [Name], My Profile / Logout and if not we show Register / Login.
Comments: We display the comments made for that article.
Track User Behavior: We track every single action made by users on the site
Now the only way we could think of doing this is through AJAX calls:
$('#usercheck').load(<?php echo "'" . base_url() . "ajax/check_header'"; ?>);
And so on.
This is creating a massive load on CPU, but what would be the right/alternative way of approaching this?
Please see attached:

First of all, you do not have to use AJAX for every possible dynamic content, especially in the case of comments, you may as well load them via an iframe.
That way, you are not relying on Javascript to make the request.
It may even work for the counter.
However, you problem is not Javascript, nor the database server, based on what I can see from your graph. It seems to me you have some heavy PHP controllers, maybe you are loading a heavy framework just to have $session->id checked.
Further, what do you mean by "we track every single action"? How do you track them? Are you sending an AJAX request from every little thing or are you debouncing them with JS and only sending them one every 30 seconds or so?
My advice is that you consider the size of the PHP code you are calling, and slim it down as much as you can, even to zero if it seems feasible (by leveraging localStorage to keep track of you user session after the first login), and maybe loading the counter and the comments in alternative ways.
For example, I infer you are only checking the counter once per page load, ignoring subsequent loads by other users while the current user is reading the article, so your counter may happen to be out-of-date once i a while, depending on your traffic.
I going to explain it better: your page has n views, so when I load it, you request for n and then display n+1 to me. While I'm reading, the same page gets requested and viewed x times by other users. Your counter on the server has been surely updated to n+x, but the counter on my page still says "n views".
So, what's the point in being picky and showing n+1 to me and the not updating it, thus being off by x?
So, first of all the counter controller should be as slim as possible, and what if you loaded it within an iframe, auto updating without AJAX?
How to refresh an iframe not using javascript?
That would keep the counter up-to-date, you may render it with PHP just once per page view, and then just statically serve the resulting HTML file.

Passing a variable from one page to the next page

I am developing a Question & Answer website where a user is presented five puzzles on a page and the score is calculated using JavaScript as he attempts the questions on the page. The score is saved in a Javascript variable score. I have a paging system like this:
Now when the user clicks on 3 I want to send the variable score to the next page, where I have require scoreUpdateInDatabase.php on each such page such that the score of previous page is made permanent to the databse and the following PHP script presents him the next 5 questions.
How can I pass that score variable in secure way? I can't use GET because the user will modify it. I am satisfied with POST if this can be used, even though POST data can be modified but I just want minimal security.
P.S. Please do not suggest making AJAX call where in one side I will send score and while returning carries next 5 questions. I don't want to use AJAX to refresh content because it is not SEO friendly.

The simplest solution would be cookie based. Writing the value to a session cookie and the reading it.
You could use jquery cookie. It also gives you the option to require https if desired.

Save it in a session. POST would work equally well in this particular case but my preference would be storing it in the session.

The only secure way to do this is to pass the actual answers to the server using a POST or AJAX, do the calculation of the score also on server side and keep it in a SESSION variable.
More information on sessions in PHP

Try looking into Jquery - You should be able to return the value to the server scripting language (as you listed PHP as a tag, I assume you're using PHP). By using Jquery, you can get the javascript variable to the form BEFORE submitting the form to the next page.
Assuming you have used PHP to generate the form to submit initially rather than create the form in javascript. I would use Jquery - to get this file ( http://jquery.com/ ) and to include("jquery.js"); etc... in your PHP script for it to be used.
I would then convert the javascript variable(s) to a php variable and assign this to a hidden field in the form to be submitted to the next page using a $_POST[] variable.

However It will not be SEO friendly (POST and SESSION is not SEO friendly, but you should use them, continue reading)
We are talking of a game. No-one want that the Search engine index the last page of a game... because everyone can search on google (for example) for the last page of your game without playing.
You have to use ajax or post, but don't let google index every page of your game. It's nonsense.
Only the first page of your game should be indexed.

dynamic marking changing content JavaScript

I created a table that receives data from a SQL database to a PHP script that parse this back though my AJAX to the HTML page.
With this information I create the table.
It works and the beauty of it: every time the data changes the table changes.
BUT: it reloads the whole table with new data.
What I want is to have it only reload the part that's been updates and then "mark" it until you mouse over it.
Is there any function in JS that allows to compare 2 JSON encoded strings and then only update the part that's not similar?
I have use jQuery but haven't found anything as of yet.I apologies for not showing any code but it's protected from sharing

You have to poll AJAX request to the server after every few seconds or minutes and see if there's any update. If so, you receive that update with say the id or index number of the data which you can replace with the new one. That way you won't have to update the entire thing.

A brief question about JavaScript or AJAX

I have been finding ways around this for a long time but think it's time I addressed it.
If I have a page that has a dropdown menu, is there anyway I can select a value which will subsequently load other values further down.
Can this be done without a page reload?
I will give you an example.
Say I was making some tools for an admin panel, but first of all they needed to select a member to work with.
They would select the member and then below, the fields about that member would be populated based on what was selected in the first menu.
As I have already asked, can this be done without a page reload?
Thanks for reading.

Yes it can be done without AJAX. When the page is rendered pass all the collections that will be used by the dropdown lists as JSON objects into the HTML:
var collection = [{ id: 1, name: 'John' }, { id: 2, name: 'Smith' }];
...
Then register for the change event of the first drop down and based on the selected value go and fetch the data from the other collections. Of course if you have lots of data this might not be practical as your pages will become very large and in this case AJAX woulld be more appropriate.

Answer YES it can be done.
Firstly you'll need an event, in this case you need to take action on the onChange event for the selectBox. So when an item changes you run a function.
Now you have 2 choices. You can do this using AJAX or NOT, it really depends on the complexity / security of your application.
In the following I refer to
Users : those using the application
Hidden Client Side Data : Data sent to the client during page load, but not visible to all users, however using view source, or downloading JS files, the Data is not secured.
Method 1 - NO AJAX
Basics: You send all the possible display options down initially when the page is first loaded, but display only the sections relevant to the user during selectbox onchange events.
Recommended when: No security condiderations if hidden client side data is detected (or won't be detected, or you simply trust your audience to use the app in the intended manner). Lastly when your total view permutations are low.
Method 2 - AJAX
Basics: You send down initially only the page skeleton, when the user changes the value of the select box, you then do an AJAX request to the server - grab the new view info thats relevant to that user, send it back down to a script which will inject that user data into the DOM.
Recommended when: You have a public site, or a site where security is a consideration. Where you have lots of view permutations or want more customizations per user than in scenario 1.
As you see both methods do not require a repost - method 1 ships everything upfront, method 2 uses AJAX to fill in data when required. Both methods are valid depending on your requirement.

Yes. Ajax is mainly used for that i.e. (without a page reload)
You have to use following step to achieve
Create a link and call a JavaScript function on it's onchange function
In the JavaScript function you have to call Ajax request.
Update the div in your ajax response.