var xhr = [];
var progress = [];
var totaldata = [];


for (i = 0; i < 5; i++) {
  (function(i) {
    var start = new Date().getTime();
    xhr[i] = new XMLHttpRequest();
    url = "/" + "?n=" + Math.random();
    xhr[i].open("POST", url, true);
    xhr[i].setRequestHeader("Content-Type", "text/plain;charset=UTF-8");
    xhr[i].upload.addEventListener("progress", createProgressHandler(start, i), false);
    xhr[i].send(UploadData);
    // Initialize progress:
    progress[i] = { bytes: 0 };
};

function createProgressHandler(start, i) {
    return function (event) {
      end = new Date().getTime();
      time = (end - start) / 1000;
      var duration = time;
      var bytes = event.loaded;

      progress[i] = event.loaded;

      var sumofcurrentdata = ((parseFloat(progress[0])) + (parseFloat(progress[1])));
	  totaldata.push(sumofcurrentdata);
    }
}

"sumofcurrentdata" is get reset when new function initialize. How can i keep add sumofcurrentdata?