What to do with javascript connection on a multi-page site?

Question

PHP

Good afternoon. I am developing a multi-page website. Faced such problem:
On the main page I have a slider (carousel). An es6 module is connected to the common script, in which keystrokes are caught. Everything works, but on other pages where there is no this carousel, an error pops up in the console "Cannot read property 'addEventListener' of null". How to decide? Perhaps there is a way to connect modules depending on the page?

Answer 1

In the handler write:

$json = $_POST['data']; //json need to be data
    $info = json_encode($json);
    $file = fopen('test.json','w+') or die("File not found");
    fwrite($file, $info);
    fclose($file);
  exit;

file_put_contents('test.json', json_encode($_POST['data']));
  exit;

You need to convert the array to json object and write this line.

Answer 2

As always

document.querySelector('.reviews_next') && document.querySelector('.reviews_next').addEvent..........