File Upload with Ajax

gistfile1.js

$form = $("#edit_item");

// Build the FormData object with some Rails-specific attributes
var formData = new FormData($form[0]);
formData.append('utf8','✓')
formData.append('_method', 'put'); // editing existing record
formData.append('authenticity_token', AUTH_TOKEN);

$.ajax({
  url: $item.attr('data-uri'), // or # form action attribute
  type: 'POST',
  data: formData,
  
  xhr: function() {
      myXhr = $.ajaxSettings.xhr();
      if (myXhr.upload){ // check if upload property exists
          myXhr.upload.addEventListener('progress',function(e) {
            if (e.lengthComputable){
                console.debug({value:e.loaded,max:e.total});
            }
          }, false); // for handling the progress of the upload
      }
      return myXhr;
  },
  
  success: function() { console.debug("success"); },
  error: function() { console.debug("error"); },
  //Options to tell JQuery not to process data or worry about content-type
  cache: false,
  contentType: false,
  processData: false
});