Develop Reference

can AJAX do anything else than load a JSON file?

I'm want to (or think I need to) use AJAX to accomplish what I intend.
When clicking on a specific link in a list of links, I want to fill the HTML markup below with content of specific subpages. The data is naturally somewhere in the database and actually easily accessible with the CMS's API (I'm using Processwire).
I'm quite new to coding and especially AJAX and all documentation I find online only mention it in combination with a JSON file that would be loaded via AJAX.
However, I don't have a JSON file on the server, that means, according to my understanding, I would need to
store the data I need in a multidimensional php array,
use json_decode to create and then save that JSON-file on the server,
load that file via AJAX and process through more JS.
Let alone keep that JSON-file updated (or create a new one and delete the old one?) since new content will arrive periodically. It seems unnecessarily complicated to me, but what do I know.
There's got to be a better way…
Any help is appreciated.

AJAX is simply a way to make a request to the web server for information.
When you make an AJAX request you ask for a response from a file on a server. So, you can send an AJAX request to a PHP script for-instance.
The PHP script could return anything, JSON is common and very widely used response format, but XML might be another one you've encountered.
So, your request for information is made using AJAX, and the response you get back is JSON.
You don't need to store a JSON file on your server. You just need to make an AJAX request that returns current data in JSON format.

AJAX allows you to do asynchronous HTTP requests.
You can of course ask for a json file, but you can also (for example) call an API.
I suggest you start by reading the the getting started guide for AJAX in MDN:
https://developer.mozilla.org/en-US/docs/Web/Guide/AJAX/Getting_Started

Is JSON not serialise-able over http or Django doesn't know how to read it?

I have created a couple of projects with Django.
Every time I try to send an ajax POST request from frontend to django, I have to use JSON.stringify() function, pass it inside the body of POST request and parse the JSON manually inside Django (using ujson, because of its faster).
My question is that why do I need to do this manually?

PHP/AJAX Requests: session_start(): Cannot send sesssion cache limiter - headers already sent

I have a problem which I can not find a solution to:
After a mouse keypress (onclick="") in my web application, I call a PHP function via AJAX request. This is nothing unusual. However, the PHP function needs to access some session variables. As I call the PHP function via HTML5 onclick and AJAX request, the webpage is already rendered, which probably means the headers have already been sent.
Probably, as a result of that, I get the following error:
session_start(): Cannot send session cache limiter - headers already sent
The key information here is that my PHP function called through AJAX Request does not output anything to the browser before calling session_start().
Is there any solution to this, please? Originally, I thought, AJAX function calls are independent from rendering the webpage and I could basically call session_start() at any time via AJAX. But now, it looks to me, that I can not call session_start() from my PHP function if called with AJAX request, just because all the AJAX calls are performed after rendering the webpage and thus after sending the headers?
Client Side: HTML5, JavaScript (no jquery)
Server Side: PHP, MySQL
If you have any idea for a workaround, that would help. Because of security reasons, I do not want to pass needed parameters as POST arguments. Because of speed reasons, I do not want to access them from my MySQL database. I would really like to know, if there is a way to access session variables through AJAX calls.
What I would like to know, if it is possible to replace AJAX calls with local PHP function calls. Then, I could take advantage of PHP global variables.
Thank you.

Call JS through cURL

I am trying to call my js file through cURL. That JS file in-turn call's third party API to fetch me the result.
Overview of JS file.
In js file i am creating an object of the 3rd party library file and sending them the relevant data to get the response back. This response need to be captured and returned back when call'd through cURL.
Procedure of calling cURL
The cURL function will be triggered as an API call.
What i have tried so far !
I am storing the response of the library file in a cookie. So that i can use the same. I am able to achieve this through browser. But, when tried with REST client, i get all my <script> function as response also it doesn't call the library file too.
So, how can i call the JS file through cURL OR is there any other alternative way to achieve this. ?
NOTE : It is not a regular browser flow, it has to be a API call.
Please let me know on this !

what's the diffrence between $.ajax / $.get / $.POST / .load()?

I'm trying to understand AJAX and JSON and I'm not sure I get it, there are methods and functions that are doing the same stuff...
You've got $.getJSON to retrieve JSON format data from server, and you have $.ajax + $.post + $.get + load() to send data data to the server?
Can I use all of those methods to send JSON data?
Really I'm confused! Help me figure this out.

All those are just shorthands for calling the $.ajax function.
load is for retrieving HTML and writing it to the DOM in one go. You want to load JSON.
get and getJSON use GET requests which are not well-suited for sending JSON data.
post does a POST request, but doesn't allow you to choose the contentType of the sent data
For sending JSON you should use the $.ajax function with its many options, see Send JSON data with jQuery.

An AJAX request is, at heart, an HTTP request. This is the same protocol which is used for all content on the Web (arguably, if it's not HTTP, it's not the Web) - loading a page, the images on the page, the CSS and JS includes, a submitted form, etc, etc.
As such, it inherits pretty much all of the flexibility of HTTP, meaning a generic function like jQuery.ajax ends up quite complex, with lots of options you don't normally need to worry about. This leads to the Shorthand Methods you mentioned, which bundle up common sets of options and functionality.
Among the things you might want to vary:
The "method" of the request: GET or POST (or less common ones like HEAD, PUT, DELETE...). A GET request is the simplest: request this URL, give me its contents; parameters to a GET request are shoved onto the "query string" of the URL. A POST request is how larger forms would be submitted on a normal page: the parameters are passed as a body of data separate from the URL and control headers; for an AJAX request this is often helpful to send a block of XML or JSON to a URL. This is a very broad overview, and there are many more distinctions in behaviour and meaning between the two.
The "content type" you want in the response (and, for a POST request, of the data you're sending). Not only does this tell both the server and the browser what data it is handling, ensuring it will pass it successfully, it can give jQuery (or whatever library) a hint of what to do next: if a call returns XML, you'll probably want to manipulate it as a DOM straight away; if it's JSON, you'll want to parse it as a JS object.
What you want to do once the data comes back. I've already mentioned parsing JSON or XML, but what if your response is actually a block of HTML that you want to inject straight into the parent page? Obviously you could do that yourself in the callback function, but again jQuery includes a shorthand form in the shape of .load().
All of the above are possible with jQuery.ajax, but you'd have to remember the parameters, even though you're falling into the same cases again and again, so chances are most of the time you'll be using whichever of the shorthands suits your needs at that moment.