var ajax = {
  request: 0,
  callUrl: function(params, callback)
  {
    var url = config.file_ajax;
    var char="?";
    for (i =0; i < params.length ; i+=1)
    {
      url = url + char + params[i][0]+'='+params[i][1];
      char = "&";
    }
    
    if(window.XMLHttpRequest) {
      this.req = new XMLHttpRequest();
    } else if(window.ActiveXObject) {
      this.req = new ActiveXObject("Microsoft.XMLHTTP");
    }
    
    this.req.open("POST", url, true);
    this.req.onreadystatechange = callback;
    this.req.send(null);  
  }
}