Using the $loop variable ( The new $loop variable in Laravel 5.3 ) inside of a loop it’s easy to check when you're at the start or the end of a loop. In this case show a comma for all items except the last one we can use:

! $loop->last

Which says then the loop is not the last item, at which points add the comma and close it with an endif.

@foreach($items as $item)

    {{ $item }}@if (!$loop->last),@endif

@endforeach