REST Service Poller based on Web Workers and XMLHttpRequest object

poller.js

var Ajax = {

  httpRequest : null,

  initXmlHttpObject : function() {
    'use strict';

    if (XMLHttpRequest) { // Chrome, Mozilla, Safari, ...
      this.httpRequest = new XMLHttpRequest();
    } else
      if (ActiveXObject) { // IE
        try {
          this.httpRequest = new ActiveXObject("Msxml2.XMLHTTP");
        }
        catch (e) {
          try {
            this.httpRequest = new ActiveXObject("Microsoft.XMLHTTP");
          }
          catch (e) {}
        }
      }
    },

  sendRequest : function(config) {
    'use strict';

    if (!this.httpRequest) { //reuse the same object
      this.initXmlHttpObject();
    }

    var req = this.httpRequest;

    if (!req) {
      return;
    }

    req.open('GET', config.url + '?' + this.stringifyParams(config.options), true);
    //req.setRequestHeader('User-Agent','XMLHTTP/1.0');

    req.onreadystatechange = function() {
      if (req.readyState !== 4) {
        return;
      }
      if (req.status !== 200 && req.status !== 304) {
        config.error();
        return;
      }
      config.success(req);
    };

    if (req.readyState === 4) {
      return;
    }

    req.send();
  },

  stringifyParams : function(params) {
    'use strict';
    var keys = Object.keys(params),
        i,
        l,
        s = [],
        value;
    for (i = 0, l = keys.length; i < l; ++i) {
      value = (params[keys[i]] == null) ? '' : params[keys[i]];
      s[s.length] = encodeURIComponent(keys[i]) + '=' + encodeURIComponent(value);
    }
    return s.join('&').replace(/%20/g, "+" );
  }
};
var Poller = (function() {

  'use strict';

  return {
    // number of failed requests
    failed: 0,
    // starting interval (1000 === 1 second)
    interval: 10000,

    timer: null,

    url: null,

    options: null,

    // kicks off the setTimeout
    init: function(){
      if (this.timer) {
        clearTimeout(this.timer);
      }
      this.timer = setTimeout(
        this.getData.bind(this), // ensures 'this' is the poller obj inside getData, not the window object
        this.interval
      );
    },

    stop: function() {
      clearTimeout(this.timer);
    },

    // get AJAX data + respond to it
    getData: function(){
      Ajax.sendRequest({
        url: this.url,
        options: this.options,
        success: this.successHandler.bind(this),
        error: this.errorHandler.bind(this)
      });
    },

    successHandler : function(res) {
      self.postMessage(res.response);
      this.init();
    },

    // handle errors
    errorHandler: function(){
      if( ++this.failed < 10 ){
      // give the server some breathing room by
      // increasing the interval
      this.interval += 1000;
        // recurse
        this.init();
      }
    }
  };
}());

//Handle communication with web worker
self.addEventListener('message', function(e) {
  'use strict';
  var data = e.data;
  switch (data.cmd) {
    case 'start':
      Poller.url = data.url;
      Poller.options = data.options;
      Poller.init();  //start polling
      break;
    case 'stop':
      Poller.stop(); //clears the timeout
      self.close(); // Terminates the worker.
      break;
    case 'updateConfig':
      if (data.url) {
        Poller.url = data.url;
      }
      if (data.options) {
        Poller.options = data.options;
      }
      break;
    default:
      self.postMessage('Unknown command: ' + data);
  }
}, false);