I am trying to upload multiple files to Google Drive using the app script and the code that I use does just that but it requires users to select all their files in one field and upload them all at once.

Is there a way to create multiple fields for each file and upload them all at once?

I am asking this question because many users might not select all the necessary files while using one field to upload their files but with a field for each file that mistake can be prevented.

I know little about app scripts and the code that I present with this question is not my work but I will be glad if anyone can help with a solution.

To better understand the app script; What it does is that it creates a parent folder in google drive with the name and email address provided by the user and it saves all their files in that folder.

See the code below;

function doGet() {
    return HtmlService.createHtmlOutputFromFile('Form').setSandboxMode(
            HtmlService.SandboxMode.IFRAME);
}

function createFolder(parentFolderId, folderName) {
    try {
        var parentFolder = DriveApp.getFolderById(parentFolderId);
        var folders = parentFolder.getFoldersByName(folderName);
        var folder;
        if (folders.hasNext()) {
            folder = folders.next();
        } else {
            folder = parentFolder.createFolder(folderName);
        }
        return {
            'folderId' : folder.getId()
        }
    } catch (e) {
        return {
            'error' : e.toString()
        }
    }
}

function uploadFile(base64Data, fileName, folderId) {
    try {
        var splitBase = base64Data.split(','), type = splitBase[0].split(';')[0]
                .replace('data:', '');
        var byteCharacters = Utilities.base64Decode(splitBase[1]);
        var ss = Utilities.newBlob(byteCharacters, type);
        ss.setName(fileName);

        var folder = DriveApp.getFolderById(folderId);
        var files = folder.getFilesByName(fileName);
        var file;
        while (files.hasNext()) {
            // delete existing files with the same name.
            file = files.next();
            folder.removeFile(file);
        }
        file = folder.createFile(ss);
        return {
            'folderId' : folderId,
            'fileName' : file.getName()
        };
    } catch (e) {
        return {
            'error' : e.toString()
        };
    }
}
<!DOCTYPE html>
<html>
<head>
<base target="_top">
</head>
<body>
    <form id="uploaderForm">
        <label for="uploaderForm">Upload multiple Files</label>
        <div>
            <input type="text" name="applicantName" id="applicantName"
                placeholder="Your Name">
        </div>
        <div>
            <input type="text" name="applicantEmail" id="applicantEmail"
                placeholder="Your Email">
        </div>
        <div>
            <input type="file" name="filesToUpload" id="filesToUpload" multiple>
        <input type="button" value="Submit" onclick="uploadFiles()">
        </div>
    </form>
    <br>
    <br>
    <br>
    <br>
    <br>
    <br>
    <div id="output"></div>
    <script>
        var rootFolderId = '1J8UvFldmZQsVE_XaRo7CTYts7PDlSeWw';
        var numUploads = {};
        numUploads.done = 0;
        numUploads.total = 0;
        // Upload the files into a folder in drive
        // This is set to send them all to one folder (specificed in the .gs file)
        function uploadFiles() {
            var allFiles = document.getElementById('filesToUpload').files;
            var applicantName = document.getElementById('applicantName').value;
            if (!applicantName) {
                window.alert('Missing applicant name!');
            }
            var applicantEmail = document.getElementById('applicantEmail').value;
            if (!applicantEmail) {
                window.alert('Missing applicant email!');
            }
            var folderName = applicantName + ' ' + applicantEmail;
            if (allFiles.length == 0) {
                window.alert('No file selected!');
            } else {
                numUploads.total = allFiles.length;
                google.script.run.withSuccessHandler(function(r) {
                    // send files after the folder is created...
                    for (var i = 0; i < allFiles.length; i++) {
                        // Send each file at a time
                        uploadFile(allFiles[i], r.folderId);
                    }
                }).createFolder(rootFolderId, folderName);
            }
        }

        function uploadFile(file, folderId) {
            var reader = new FileReader();
            reader.onload = function(e) {
                var content = reader.result;
                document.getElementById('output').innerHTML = 'uploading '
                        + file.name + '...';
                //window.alert('uploading ' + file.name + '...');               
                google.script.run.withSuccessHandler(onFileUploaded)
                        .uploadFile(content, file.name, folderId);
            }
            reader.readAsDataURL(file);
        }

        function onFileUploaded(r) {
            numUploads.done++;
            document.getElementById('output').innerHTML = 'uploaded '
                    + r.fileName + ' (' + numUploads.done + "https://stackoverflow.com/"
                    + numUploads.total + ' files).';
            if (numUploads.done == numUploads.total) {
                document.getElementById('output').innerHTML = 'All of the '
                        + numUploads.total + ' files are uploaded';
                numUploads.done = 0;
            }
        }
    </script>
</body>
</html>