问通过javascript中的API调用下载文件

EN

$filename = "Export file";
$delimiter = "\t";
$output = fopen('php://output', 'w');
fwrite($output, "sep=\t" . PHP_EOL);

// ... put stuf in document

fclose($output);

header('Content-Description: File Transfer');
header('Content-Disposition: attachment; filename=' . $filename . '.csv');
header('Content-Type: text/csv; charset=utf-8');
header('Expires: 0');
header('Cache-Control: must-revalidate');
header('Pragma: public');
echo $output; // also tried readfile($output) but it triggers an error that it needs a valid path