如何在通过post发送之前检查错误文件输入

Question

In the web page I have 2 tabs and 1 submit button. I first tab inputs with type=text. In second inputs with type=file. I wanna to send both tabs with 1 submit. But problem isn't here. In the second tab I need to check files for error before sending them. So If it has an error then submit button isn't active. How can I do this? Now I check them for error only after sending them. And when some of the files have an error then upload fails and its return to page with an error. And all other files which haven't error disappear from the input . First tab http://prntscr.com/mnzc79 . Second tab http://prntscr.com/mnzca3 . Here all inputs are the document of the student in university. So I can use just multi upload. Because all of them are a different files. I can't understand the mechanism of uploading many file inputs with error check. Here my code

            Check if text inputs uploaded. If files were set then I push them to the array to use in query.

            if(!empty($_POST["first_name"])){
                $keys=$keys."first_name,";
                $first_name=$_POST["first_name"];
                $values=$values."'".$_POST['first_name']."',";
            }
            if(!empty($_POST["last_name"])){
                $keys=$keys."last_name,";
                $last_name=$_POST["last_name"];
                $values=$values."'".$_POST['last_name']."',";
            }
            ...
            ...

            Check if files uploaded 
            if(isset($_FILES["zayavlenie_o_zachisleniy"]["name"])  && !empty($_FILES["zayavlenie_o_zachisleniy"]["name"])){
                array_push($uploads,"zayavlenie_o_zachisleniy");
                upload("zayavlenie_o_zachisleniy");
            }
            ...
            ...
            Here checks file for error and upload
            function upload($filename){
                    if (!file_exists('student_docs/'.$first_name.'_'.$last_name.'_'.$otchestvo)) {
                        mkdir('student_docs/'.$first_name.'_'.$last_name.'_'.$otchestvo, 0777, true);
                    }
                    $target_dir = 'student_docs/'.$first_name.'_'.$last_name.'_'.$otchestvo.'/';
                    $target_file = $target_dir . basename($_FILES[$filename]["name"]);

                    $uploadOk = 1;
                    $imageFileType = strtolower(pathinfo($target_file,PATHINFO_EXTENSION));
                    // Check if image file is a actual image or fake image
                    if(isset($_POST["submit"])) {
                       .....
                    }
                    // Check if file already exists
                    if (file_exists($target_file)) {
                        .....
                    }
                    // Allow certain file formats
                    if($imageFileType != "jpg" && $imageFileType != "png" && $imageFileType != "jpeg"
                        .....
                    }
                    // Check if $uploadOk is set to 0 by an error
                    if ($uploadOk == 0) {
                        .....
                    } else {
                        if (move_uploaded_file($_FILES[$filename]["tmp_name"], $target_file)) {

                            array_push($values,$target_file);
                            echo "The file ". basename( $_FILES[$filename]["name"]). " has been uploaded.";
                        } else {
                            echo "Sorry, there was an error uploading your file.";
                        }
                    }

                }

                $sql="UPDATE   students set $set where id='$student_id'";

                for($i=0;$i<sizeof($uploads);$i++){
                    if($i==(sizeof($uploads)-1)){
                        $sql=$sql."'".$uploads[$i]."'";
                    }
                    else{
                        $sql=$sql."'".$uploads[$i]."',";
                    }
                }
                $db->insert($sql.")");

Answer 1

You can either do this with javascript or php. If you are checking if the file does already exist on your webserver, you can't do this ONLY using javascript. So you need to check this with php, cause php is running on your server. Javascript not.

So, when you encounter any error while uploading the files (like already existing files or wrong file formats) you can redirect the user to any page you want and cancel the request like this:

header("Location: http://YourErrorPage.com");
exit;