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Jquery $.post html to external php and print the html as pdf. Need to find optimal solution

I get mysql data.
Create - echo the mysql data as html.
If visitor wants to print the data as pdf (i mean to create pdf file and save on computer), i with jquery take the data and send to external php file. In the external php file, using http://www.tcpdf.org solution i want to create pdf file (on fly, only as variable; i do not want to save the file on my server) so that user can save it.
User remains on the same url, just after user clicks button, i offer the user to save rendered pdf. I do not want to change url or add html content to the url (like print_pdf.php?html_content).
At the moment i use code like below.
<div id="to_print_as_pdf">
<div>Some content from mysql</div>
<table>Another content from mysql</table>
</div>
<button type="button">Click to print as pdf</button>
<span id="result_print_pdf"></span>
Jquery to send the data
<script>
$("button").click(function(){
$.post('_prepare_to_print_pdf.php',
{ content_to_print: $('#to_print_as_pdf').html() },
function(result_print_pdf) {
$('#result_print_pdf').html(result_print_pdf).css('color', 'black');
});
});
</script>
File _prepare_to_print_pdf.php
$_SESSION['content_to_print'] = trim($_POST['content_to_print']);
<script>
window.location.href = "https://www.example.com/_print_pdf.php";
</script>
File _print_pdf.php
//Use http://www.tcpdf.org solution
$html = $_SESSION['content_to_print'];
$pdf->writeHTMLCell(0, 0, '', '', $html, 0, 1, 0, true, '', true);
$pdf->Output('example_001.pdf', 'I');
How to do the same without _prepare_to_print_pdf.php? Above solution waste server resources (creating session).
I tried with $.post to send html content directly to _print_pdf.php, but in such case instead of prompting to to save pdf file, i see "garbage" characters...
Solution at the moment
May be will help to someone
$('#for_hidden_form_for_print_pdf').append('<form action="_print_pdf.php" method="post" target="_blank" id="hidden_form_for_print_pdf">' +
'<textarea id="content_to_print" name="content_to_print">html content to send </textarea>' +
'<div><button style="display: none;" id="btn_to_print_pdf">Print pdf</button></div></form>');
$('#btn_to_print_pdf').trigger('click');
$( "#hidden_form_for_print_pdf" ).remove();
So when visitor clicks button/icon, i take necessary html data, insert into textarea id="content_to_print". Then trigger click for btn_to_print_pdf, then remove appended form. So i send to external php file, necessary html code. In php file i process the html code, create content for pdf file and print.

I want to change the main content dynamically with javascript instead of individual pages

My website is currently using .tpl template files to load different pages dynamically. That will load an entire page again, so header, sidebar (chat), main content and the footer.
In my index.php file there is a switch case which loads the page 'home' when you click on 'home' in the menu. (example)
But I don't want that. Because their is also a chat in the sidebar, and that reloads/resets eveytime you load a different page. So all previous messages will be gone. So what I do want is changing only the main content part. So header, sidebar and footer will stay and won't reload.
I tried to do it with javascript but that didn't work...
Can someone help me or atleast put me on the right path?
(And yes, I have been searching for the last hour on stackoverflow and google but couldn't find anything...)

What you need is called AJAX(With Ajax, web applications can send data to and retrieve from a server asynchronously (in the background) without interfering with the display and behavior of the existing page.)
To use ajax u need Javascript to send the request to a PHP file that loads the smarty template that contains your main content and insert the html code back into the page:
<?php
//some-php-file.php
include("Smarty.class.php");
$smarty = new Smarty;
$smarty->display("main_content_part.tpl");
?>
//link on 'home' site
Home
//javascript(jquery) ajax request
$('#ajaxHomeBtn').click(function(e){
e.preventDefault();
$.get("some-php-file.php", function(smarty_html_data) {
$(".main-content").html(smarty_html_data);
});
});

Please follow following instruction :
Create separate .tpl file for header,footer,sidebar and contents files.
In main file include header,footer,sidebar and left one section for content.
3.Replace your .tpl (using id or class) file content using ajax call.
bind your url with function.
Sample code as below:
// sidebar.php
<ul>
<li><a onclick="changePage(this)" data-page="home.tpl">Home</a></li>
<li><a onclick="changePage(this)" data-page="aboutus.tpl">About Us</a></li>
</ul>
// master.php
<?php
include("header.php");
include("sidebar.php");
?>
<section id="fileContent">
</section>
<?php include("footer.php");
?>
<script href="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.1.1/jquery.min.js"></script>
<script>
function changePage(obj)
{
var Filename=$(obj).data('page')
$.get(Filename, function( data ) {
$( "#fileContent" ).html(data);
});
}
</script>

How can i call from php and write the result in a specific place in html code without the need of passing variables

I am facing a situation that I don't know how to proceed I will try to be clear about what I want to do: here it goes I have 2 files one called index.php (where it's almost all of it HTML code) other indexphp.php where I'm handling PHP code, connecting to DB etc.
here's a print screen of my index.php, this is supposed to be a dashboard that you access after logging in in the application (where I am nesting my HTML code)
dashboard
I am using this
if (!isset($_SESSION['nivel_user'])){
header('Location: /php/logout.php');
} else {
$tu = $_SESSION['nivel_user'];
$userid = $_SESSION['idformador'];
$username = $_SESSION['user'];
}
Session variables in both index.php and indexphp.php and I want it to show different queries according to my login (I have different types of access levels) the results of my queries are supposed to be shown in that dashboard instead of those numbers you see at the top of that print screen, right now there are static values and I want them to be dynamic according to my queries.
I tried something like this but it doesn't work. (Note: Those queries need to be updated on page load since after logging in I automatically access the dashboard)
$(document ).ready(function(){
$('#query1').load('indexphp.php'){
<div class="row tile_count">
<div class="col-md-2 col-sm-4 col-xs-6 tile_stats_count">
<span class="count_top"><i class="fa fa-user"></i> </span>
<div class="count" id="query1">2</div>
<span class="count_bottom"><i class="green">100% </i> </span>
</div>

Python interaction with browser (Raspberry WebioPi)

I use a tool called "webiopi" to control a wellness device via a Raspberry pi and a relay board. This tool connect buttons on a webpage with a Python script.
I can read the state (low/high) from the GPIO pins on the buttons i've created.
What i want is to show values from the script in the browser.
(Like ' temperature_measured' or. 'Calculated_time')
Is there a way i can show output from the python script to the webbrowser?
button = webiopi().createMacroButton("macro", "Normaal", "Prog1");
$("#top").append(button)
<div id="content" align="center">
<td>
</td>
{{print here output from script.py}}
<div id="top"></div>
</div>
</div>

You could use PHP to call the script and echo the output to the page. You'll need PHP installed and enabled, and the file must end with .php. If you know the webserver you are using, I can give you some additional help. Also note that the script should print all information it wants on the web page into standard output.
button = webiopi().createMacroButton("macro", "Normaal", "Prog1");
$("#top").append(button)
<div id="content" align="center">
<td>
</td>
<?php exec("python myscript.py", $out); echo $out; ?>
<div id="top"></div>
</div>
</div>

In a this forum [Wpio forum][1]https://groups.google.com/forum/#!topic/webiopi/DreW_74gm0o
gives Pete Dudash the answer to this question, which i copy here
Yes, this is possible. What you’re looking to do is add a callback routine to your javascript. First you execute some action in javascript (either from a button press or a timer) and call a python macro. This time, you specify a call back routine when calling the macro. The call back routine receives data from the macro and then you can do whatever you want with it.
Javascript:
function getPythonResponse() {
// "sendData" is the name of the macro you specify in your script.py
// "[]" is an empty list. If you want to send data for the macro to use, you would include that here
// "handlePythonResponse" is the name of the callback routine that will execute once the python macro is finished
webiopi().callMacro("sendData", [], handlePythonResponse);
}
var handlePythonResponse = function(macro, args, response) {
// "response" is the variable that holds the data from script.py
// Now we can apply those results to the webpage by assigning the value to the "pythonResult" id. This is the element in your HTML where you want to print the info.
$("#pythonResult").text(response);
}
Python:
#webiopi.macro
def sendData():
HTML:
<div id="content" align="center">
<td></td>
<span id="pythonResult">{{print here output from script.py}}</span>
<div id="top"></div>

How to get information from Javascript to MySQL database using PHP?

(NEWBIE ALERT)
Hello! I am working on developing a database that stores information that people enter onto these online surveys. I don't have experience with Javascript, but I have worked with PHP and MySQL before. I am currently stuck on how to store the data to the database. Here are a few things about the code:
The person that created the online surveys had the online surveys written in Javascript (saved as HTML files)
Each survey is written in a separate file
Each survey has multiple data to be stored
Every time the user hits the next button, it goes to another page of the survey
I've worked on a project similar to this before, but my forms were only a page, so whenever the user clicks the "Submit" button, I had it go to another webpage written in a separate PHP file (kind of like a "results" page).
WHAT I DON'T UNDERSTAND/NEED HELP ON:
How do I make this so that when the user hits the "Next" button, it not only goes to the next page (what it's doing right now), but also sends the info to be stored in the database?
These surveys should be filled by people on their own computers so the surveys are written in JS (client-side). The storing part should be written in PHP (server-side) and MySQL, correct? Does this mean that I have to create a separate PHP file to create the code for transferring the data to the database or can it all be done in the same file? (I would think that I would need to create a separate file, one for each survey.)
Here's a general structure of how the HTML file:
<!DOCTYPE html>
<html>
<head><link rel="stylesheet" type="text/css" href="survey.css">
<script>
function Q2(){
document.getElementById("Q").innerHTML = "does something...<button type='button' onclick='Q3()'>Next</button>";
function Q3(){
document.getElementById("Q").innerHTML = "does something...<button type='button' onclick='Q4()'>Next</button>";
function Q4(){
document.getElementById("Q").innerHTML = "does something...<button type='button' onclick='Q5()'>Next</button>";
//keeps going until the last question
</script>
</head>
<body>
<h1>Meeting 1</h1>
<p id="Q">Some text...<br><input type="text" name="tweet" style='height: 50px;width: 500px;'><br><br>
<button type="button" onclick="Q2()">Next</button>
</p>
</body>
</html>
I've done a bit of research and looked at a few textbooks. I think AJAX may be something that I need to use? But I'm not too sure. If possible, could someone explain to me what I should be doing? I would like to not only be able to find a solution for this, but understand it as well.
Thank you in advance!!

For sending data to a PHP page using JavaScript, I'd recommend using the jQuery framework, where you can do it in as simple a code as this:
function Q2(){
var tweet = $("input[name='tweet']").val();
$.post("your_receiving_page.php", { data : tweet }, function(response){ //POST to PHP page where $_POST["data"] is the tweet variable
//deal with PHP output here
console.log(response);
if(response=="success"){
//javascript code to go to next page etc.
}
}
}
That way, you make a PHP file called "your_receiving_page.php" (or whatever) and handle the posted data like so:
<?php
$tweet = $_POST["data"];
//do stuff with $tweet, e.g. put it in a database
//...
//then end the code with "success", which is what you're looking for in the JavaScript as a successful callback
exit("success");