How to upload a file using jQuery.ajax and FormData

When I use XMLHttpRequest, a file is correctly uploaded using FormData. However, when I switch to jQuery.ajax, my code breaks.

This is the working original code:

function uploadFile(blobFile, fileName) {
    var fd = new FormData();
    fd.append("fileToUpload", blobFile);
    var xhr = new XMLHttpRequest();
    xhr.open("POST", "upload.php", true);
    xhr.send(fd);
}

Here is my unsuccessful jQuery.ajax attempt:

function uploadFile(blobFile, fileName) {
    var fd = new FormData();
    fd.append("fileToUpload", blobFile);
    var xm = $.ajax({
        url: "upload.php",
        type: "POST",
        data: fd,
    });
}

What am I doing wrong? How can I get the file to be uploaded correctly, using AJAX?

You have to add processData:false,contentType:false to your method, so that jQuery does not alter the headers or data (which breaks your current code).

function uploadFile(blobFile, fileName) {
    var fd = new FormData();
    fd.append("fileToUpload", blobFile);

    $.ajax({
       url: "upload.php",
       type: "POST",
       data: fd,
       processData: false,
       contentType: false,
       success: function(response) {
           // .. do something
       },
       error: function(jqXHR, textStatus, errorMessage) {
           console.log(errorMessage); // Optional
       }
    });
}  

If you are uploading from a HTML5 form that includes an input fo type file you can just use querySelector and FormData and it works.

In case of php it will give you all files in the $_FILE and all other inputs in the $_POST array.

JS/jQuery:

function safeFormWithFile()
{
  var fd = new FormData(document.querySelector('#myFormName'));

  $.ajax({
        url:'/catchFormData.php',
        method:'POST',
        data:fd,
        processData: false,
        contentType: false,
        success:function(data){
          console.log(data);
        }
  });
}

HTML:

<form id="myFormName">
  <input id="myImage" name="myImage" type="file">
  <input id="myCaption" name="myCaption" type="text">
</form>