Hope you can write a route controller for that php file and call the route method in Javascript.
For example,
Destination file: processing.php
Create a Route like this.
Route:get('processing', ['as=>'processing', 'uses'=>'ProcessingController@index']);
create a new controller with name ProcessingController.php,
[to create a controller in command : php artisan make:controller ProcessingController]
Inside the file add the business logic in index().
Now you can call the
<script>
$(document).ready(function(){
var processing = '<?php echo URL::route('processing') ?>';
$('#example').DataTable({
"processing": true,
"serverSide": true,
"ajax": processing
});
});
</script>