Optimize JS performance by using different UID generator and remove bind statements

polyfill/XMLHttpRequest.js

                     })
                     .fetch(_method, _url, _headers, body)
       this._task
-          .stateChange(this._headerReceived.bind(this))
-          .uploadProgress(this._uploadProgressEvent.bind(this))
-          .progress(this._progressEvent.bind(this))
-          .catch(this._onError.bind(this))
-          .then(this._onDone.bind(this))
+          .stateChange(this._headerReceived)
+          .uploadProgress(this._uploadProgressEvent)
+          .progress(this._progressEvent)
+          .catch(this._onError)
+          .then(this._onDone)
 
     })
   }
     return result.substr(0, result.length-2)
   }
 
-  _headerReceived(e) {
+  _headerReceived = (e) => {
     log.debug('header received ', this._task.taskId, e)
     this.responseURL = this._url
     if(e.state === "2") {
     }
   }
 
-  _uploadProgressEvent(send:number, total:number) {
+  _uploadProgressEvent = (send:number, total:number) => {
     if(!this._uploadStarted) {
       this.upload.dispatchEvent('loadstart')
       this._uploadStarted = true
     this.upload.dispatchEvent('progress', new ProgressEvent(true, send, total))
   }
 
-  _progressEvent(send:number, total:number, chunk:string) {
+  _progressEvent = (send:number, total:number, chunk:string) => {
     log.verbose(this.readyState)
     if(this._readyState === XMLHttpRequest.HEADERS_RECEIVED)
       this._dispatchReadStateChange(XMLHttpRequest.LOADING)
     this.dispatchEvent('progress', e)
   }
 
-  _onError(err) {
+  _onError = (err) => {
     let statusCode = Math.floor(this.status)
     if(statusCode >= 100 && statusCode !== 408) {
       return
     this.clearEventListeners()
   }
 
-  _onDone(resp) {
+  _onDone = (resp) => {
     log.debug('XMLHttpRequest done', this._url, resp, this)
     this._statusText = this._status
     let responseDataReady = () => {

utils/uuid.js

 export default function getUUID() {
-  return 'xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx'.replace(/[xy]/g, function(c) {
-    let r = Math.random()*16|0, v = c == 'x' ? r : (r&0x3|0x8);
-    return v.toString(16);
-  });
+  return Math.random().toString(36).substring(2, 15) +
+        Math.random().toString(36).substring(2, 15);
 }