CSV export in laravel 5 controller

Try this version out - this should allow you to get a nice output using Response::stream().

public function export()
{
    $headers = array(
        "Content-type" => "text/csv",
        "Content-Disposition" => "attachment; filename=file.csv",
        "Pragma" => "no-cache",
        "Cache-Control" => "must-revalidate, post-check=0, pre-check=0",
        "Expires" => "0"
    );

    $reviews = Reviews::getReviewExport($this->hw->healthwatchID)->get();
    $columns = array('ReviewID', 'Provider', 'Title', 'Review', 'Location', 'Created', 'Anonymous', 'Escalate', 'Rating', 'Name');

    $callback = function() use ($reviews, $columns)
    {
        $file = fopen('php://output', 'w');
        fputcsv($file, $columns);

        foreach($reviews as $review) {
            fputcsv($file, array($review->reviewID, $review->provider, $review->title, $review->review, $review->location, $review->review_created, $review->anon, $review->escalate, $review->rating, $review->name));
        }
        fclose($file);
    };
    return Response::stream($callback, 200, $headers);
}

(Adapted from this SO answer: Use Laravel to Download table as CSV)

Try using a regular link with target="_blank" rather than using JavaScript/AJAX. Because it's a file download opening in a new tab, the user experience shouldn't be too clunky.

My approach in Laravel 5.7

/**
 * @param array $columnNames
 * @param array $rows
 * @param string $fileName
 * @return \Symfony\Component\HttpFoundation\StreamedResponse
 */
public static function getCsv($columnNames, $rows, $fileName = 'file.csv') {
    $headers = [
        "Content-type" => "text/csv",
        "Content-Disposition" => "attachment; filename=" . $fileName,
        "Pragma" => "no-cache",
        "Cache-Control" => "must-revalidate, post-check=0, pre-check=0",
        "Expires" => "0"
    ];
    $callback = function() use ($columnNames, $rows ) {
        $file = fopen('php://output', 'w');
        fputcsv($file, $columnNames);
        foreach ($rows as $row) {
            fputcsv($file, $row);
        }
        fclose($file);
    };
    return response()->stream($callback, 200, $headers);
}

public function someOtherControllerFunction() {
    $rows = [['a','b','c'],[1,2,3]];//replace this with your own array of arrays
    $columnNames = ['blah', 'yada', 'hmm'];//replace this with your own array of string column headers        
    return self::getCsv($columnNames, $rows);
}