Assuming I have a file structure like this:
/
index.php // holds db connection, login information, ...
...
/someSubSite
content_someSite.html // basic structure, texts, forms, ...
styles_someSite.css // styling of content_someSite.html
backend_someSite.php // should send answers of AJAX requests
frontend_someSite.js // sends AJAX requests
// (when a form is submitted)
...
The db connection in index.php is realized via a PDO. So, obviously, I can not directly use this db-object in backend_someSite.php because it is declared and initialized in index.php -> two different scopes, no interaction between these files.
So my question now is: What is the best way to solve this problem?
Should I just create a PDO for every php-file for every sub-site? And share login information gathered by index.php via a PHP Session?
Basically the question is: What is the best way to share information or even whole PDO and other objects between index.php and backend_some(sub)Site.php when the subsites are queried via AJAX by the frontend.
It's unclear what else is in index.php. If it is literally just as you described, you can include it in backend_someSite.php.
If it has other things, for example anything that is output to the browser, then you should make a file that contains ONLY things like connection information (I'd suggest calling it config.php) and then include this file instead (both in index.php and backend_someSite.php)