자바스크립트에서 php 함수 호출 문의

<input type="button" value="메뉴얼 다운로드" onclick="manual_file(2)" > ////////////////////////////////////////////////////////////////////////////////////// <script>function manual_file(str){    if(str==2){        alert("<?=dfile(3)?>");     }}</script> /////////////////////////////////////////////////////////////////////////////////// <?function dfile($c){    $b=$c;if($b==3){$filename = "./test.txt";                      $reail_filename = urldecode("test.txt");    $file_dir = "./manual/test.txt";  header('Content-Type: application/x-octetstream');header('Content-Length: '.filesize($file_dir));header('Content-Disposition: attachment; filename='.$reail_filename);header('Content-Transfer-Encoding: binary');$fp = fopen($file_dir, "r");fpassthru($fp);fclose($fp);    }else{        echo "실패";    }     }  ?>