estrutura exemplo download e upload via ajax com jquery

jquery_ajax_upload_download.js

$.ajax({
  type: 'POST',
  url: "/",
  data: {},
  beforeSend: function(XMLHttpRequest)
  {
    //Upload progress
    XMLHttpRequest.upload.addEventListener("progress", function(evt){
      if (evt.lengthComputable) {  
        var percentComplete = evt.loaded / evt.total;
        //Do something with upload progress
      }
    }, false); 
    //Download progress
    XMLHttpRequest.addEventListener("progress", function(evt){
      if (evt.lengthComputable) {  
        var percentComplete = evt.loaded / evt.total;
        //Do something with download progress
      }
    }, false); 
  },
  success: function(data){
    //Do something success-ish
  }
});