var net = new Object();
 
net.READY_STATE_UNINITIALIZED=0; 
net.READY_STATE_LOADING=1; 
net.READY_STATE_LOADED=2; 
net.READY_STATE_INTERACTIVE=3; 
net.READY_STATE_COMPLETE=4; 
 
// Constructor
net.CargadorContenidos = function(url, funcionLoad, funcionLoading, funcionError, metodo, parametros, contentType) {
  this.url = url;
  this.req = null;
  this.onload = funcionLoad;
  this.onloading = funcionLoading;
  this.onerror = (funcionError) ? funcionError : this.defaultError;
  this.cargaContenidoXML(url, metodo, parametros, contentType);
}
 
net.CargadorContenidos.prototype = {
  cargaContenidoXML: function(url, metodo, parametros, contentType) {
    if(window.XMLHttpRequest) {
      this.req = new XMLHttpRequest();
    }
    else if(window.ActiveXObject) {
      this.req = new ActiveXObject("Microsoft.XMLHTTP");
    }
 
    if(this.req) {
      try {
        var loader = this;
        this.req.onreadystatechange = function() {
          loader.onReadyState.call(loader);
        }
        this.req.open(metodo, url, true);
        if(contentType) {
          this.req.setRequestHeader("Content-Type", contentType);
        }
        this.req.send(parametros);
        } catch(err) {
          this.onerror.call(this);
        }
    }
  },
 
  onReadyState: function() {
    var req = this.req; 
    var ready = req.readyState; 
    if(ready == net.READY_STATE_COMPLETE) { 
      var httpStatus = req.status; 
      if(httpStatus == 200 || httpStatus == 0) { 
        this.onload.call(this);
      }
      else {
        this.onerror.call(this);
      }
    }	
    if(ready == net.READY_STATE_LOADING) { 
        this.onloading.call(this);
    }	
  },
 
  defaultError: function() {
    alert("Se ha producido un error al obtener los datos"
      + "\n\nreadyState:" + this.req.readyState
      + "\nstatus: " + this.req.status
      + "\nheaders: " + this.req.getAllResponseHeaders());
  }
}