JavaScript implementation simple ajax encapsulation example

function ajax(obj){
    var xhr = (function (){//Get xhr object, re-encapsulated in order to be compatible with ie6  if(typeof XMLHttpRequest !='undefined') {
    return new XMLHttpRequest();
  }else if(typeof ActiveXObject !='undefined') {
    var version = [
      'MSXML2.XMLHttp6.0',
      'MSXML2.XMLHttp3.0',
      ''
    ]
    for(var i in version) {
      try{
        return new ActiveXObject(version[i]);
        break;
      }catch(e){
      //Catch the error and then jump out to continue the loop      }
    }
  }else{
    throw new Error("Your system or browser does not support XHR objects!");
  }
})();//Get xhr object    //The default true is to enable asynchronous (the main difference between asynchronous and synchronization is that the subsequent scripts can continue to run when requested. If synchronous, you must complete ajax before the subsequent scripts can be run)    if( === true) {
       = function() {
        if( ==4) {
          callback();
        }
      }
    }
  var arr=[] ;
  for(var i in ) {(encodeURIComponent(i)+'='+encodeURIComponent([i]));}
   = ('&');  //Note this step. Whether it is a get/post submission, the passed in must be formatted. The final format converted into name=zhang&age=26&wedding=no  if( === 'get') {//Requested via get       = ('?') ==-1 ? +'?rand='+()+'&'+ : +'rand='+()+'&'+;
      (,,);
      (null);
  }
  if( === 'post') {//Requested via post       =+'?rand='+();
      (,,);
      ('Content-Type', 'application/x-www-form-urlencoded');//This is the type reset of the request header, and the post request must be reset;      ();
  }
  //False enables synchronization  if( === false) {callback();}
  function callback (returnTxt) {
      if( == 200){
        (returnTxt);
      }else {
      alert('Get data error!  Error code:' +  + ',error message:' + );
    }
  }
}