function Pinger() {

  this.ip = '';
  this.inUse = false;
  this.callback = null;

  //time holders
  this.start = null;
  this.end = null;

  //image object
  this.img = null;
  this.timer = null;

}

function Pinger_ping(ip, callback) {

  if(!this.inUse) {

    this.inUse = true;
    this.callback = callback
    this.ip = ip;

    var _that = this;

    this.img = new Image();

    this.img.onload = function() {_that.good();};
    this.img.onerror = function() {_that.good();};

    this.start = new Date().getTime();
    this.img.src = "http://" + ip;
    this.timer = setTimeout(function() { _that.bad();}, 1500);

  }
}

function Pinger_good() {
  
  if(this.inUse) {
    this.inUse = false;
    this.end = new Date().getTime();
    //clear the timer & img
    clearTimeout(this.timer);
    this.img = null;
    this.callback(this.ip,true, this.end - this.start);
  }

}

function Pinger_bad() {
  
  if(this.inUse) {
    this.inUse = false;
    this.end = new Date().getTime();
    //clear the timer & img
    clearTimeout(this.timer);
    this.img = null;
    this.callback(this.ip,false, this.end - this.start);
  }

}

Pinger.prototype.ping = Pinger_ping;
Pinger.prototype.good = Pinger_good;
Pinger.prototype.bad = Pinger_bad;