使用AJAX上传文件和$ _POST失败

I'm trying to upload a file and some text inside a textarea together using AJAX. I'm getting the following error in the PHP page that receives the data:

Notice: Undefined index: guion in file/path/here on line X

It means that the file is not being sent. Tried var_dump $_FILES and it output:

array(0) { }

HTML Code:

<div id="_AJAX_"></div>

<div role="form">
  <div id="fileGuionGroup" class="form-group">
    <label for="guion">Archivo Gui&oacute;n</label>
    <input id="fileGuion" type="file" name="guion">
  </div>

  <div id="txtComentarioGroup" class="form-group">
    <label for="comentario">Comentario</label>
    <textarea id="txtComentario" class="form-control" name="comentario" rows="4" placeholder="Ejemplo: Solicito que por favor se monte este curso en plataforma."></textarea>
  </div>
</div>

<button id="send_request" type="button" class="btn btn-primary btn-block" onclick="submitSolicitud(`{$cursoKey}`)"><i class="fa fa-fw fa-cogs"></i> Solicitar Montaje</button>

Javascript Code:

function submitSolicitud(cursoKey) {
  var fileGuion     = document.getElementById('fileGuion');
  var txtComentario = document.getElementById('txtComentario');

  var formGroupGuion      = document.getElementById('fileGuionGroup');
  var formGroupComentario = document.getElementById('txtComentarioGroup');

  formGroupGuion.className      = "form-group";
  formGroupComentario.className = "form-group";

  var guion      = fileGuion.value;
  var comentario = txtComentario.value;

  var formData = new FormData();
  formData.append('guion', guion);
  formData.append('comentario', comentario);

  connect = window.XMLHttpRequest ? new XMLHttpRequest() : new ActiveXObject('Microsoft.XMLHTTP');

  connect.onreadystatechange = function () {
    onRSCallback(cursoKey);
  };

  connect.open('POST', '?view=modalsMatriz&modal=montaje&id=' + cursoKey + '&action=solicitarMontaje', true);
  connect.setRequestHeader("Content-Type", "multipart/form-data");
  connect.setRequestHeader("X-File-Name", guion.name);
  connect.setRequestHeader("X-File-Size", guion.size);
  connect.setRequestHeader("X-File-Type", guion.type);
  connect.send(formData);
};

PHP Code:

case 'solicitarMontaje':

    // This is the line that has the error of undefined index.
  die($_FILES['guion']);

  try {
    if (!isset($_FILES['guion'])) {
        # Code 1: Archivo Guión Field vacía
      throw new Exception(1);
    } elseif (!isset($_POST['comentario']) || $_POST['comentario'] == "") {
        # Code 2: Comentario Field vacío
      throw new Exception(2);
    }

    $tmp_file = $_FILES['guion']['tmp_name'];
    $filename = $_FILES['guion']['name'];

    move_uploaded_file($tmp_file, 'uploads/guiones/'.$filename);

    die(0);
    //$curso->crearSolicitudMontaje($_POST['comentario']);
  } catch (Exception $e) {
      # Output message to the screen so that Ajax captures it via connect.responseText @curso_FormMontaje.js
    echo $e->getMessage();
  }
break;  # ./ case 'solicitarMontaje'

I've tried it using FormData() and Content-Type multipart/form-data but it did not work at all. Instead it was making the page be embedded inside the _AJAX_ div that shows the messages returned from the server (such as success messages, errors at some fields i.e fields that were sent empty).

This is what I get as result using FormData when clicking the submit button:

https://postimg.org/image/rsnrt3yq9/

Turns out that what was causing issues were the HTTP headers (setRequestHeader). I removed them and edited the code a little bit, here's what it looks like now fully functional:

JavaScript Code:

function submitSolicitud(cursoKey) {
  var fileGuion     = document.getElementById('fileGuion');
  var txtComentario = document.getElementById('txtComentario');

  var guion      = fileGuion.files[0];
  var comentario = txtComentario.value;

  var formData = new FormData();

  formData.append('guion', guion);
  formData.append('comentario', comentario);

  connect = window.XMLHttpRequest ? new XMLHttpRequest() : new ActiveXObject('Microsoft.XMLHTTP');

  connect.onreadystatechange = function () {
    onRSCallback(cursoKey);
  };

  connect.open('POST', '?view=modalsMatriz&modal=montaje&id=' + cursoKey + '&action=solicitarMontaje', true);

  connect.send(formData);
};       

As expected, the data is recognized by PHP as below:

• The file "guion" comes into PHP's $_FILES array ($_FILES['guion']).

• The "comentario" field (textarea) is sent inside PHP's $_POST array ($_POST['comentario']).

Finally, both HTML and PHP code stayed the same and the conclusion is that by not setting the HTTP headers they seem to take the proper value automatically so that the request processes correctly.

Here is a very simple form data example, given what you have provided:

<script>
$(document).ready(function(){
    // I don't know what your form is called...
    $('.uploader').submit(function(e) {
        // Clone the file input
        var getFileInput    =   $("#fileGuion").clone();
        // Stop form from submitting
        e.preventDefault();
        $.ajax({
            url:'/url/to/ajax/dispatcher.php',
            // Use FormData object, pass form
            data: new FormData($(this)[0]),
            processData: false,
            contentType: false,
            type: 'post',
            success: function(response) {
                // Put html back into placeholder
                $('#_AJAX_').html(response);
                // Replace the input
                $("#fileGuion").replaceWith(getFileInput);
            }
        });
    });
});
</script>
<div id="_AJAX_"></div>
<form class="uploader">
    <label for="guion">Archivo Gui&oacute;n</label>
    <input id="fileGuion" type="file" name="guion">
    <label for="comentario">Comentario</label>
    <textarea id="txtComentario" class="form-control" name="comentario" rows="4" placeholder="Ejemplo: Solicito que por favor se monte este curso en plataforma."></textarea>
    <label>
        <input type="checkbox" id="ackCheckbox"> <i>He revisado y estoy seguro de continuar con esta acci&oacute;n.</i>
    </label>
    <input type="submit" value="Upload"> 
</form>