TypeError：无法读取未定义的属性“open”（Phonegap和Ionic）

Question

I'm building a mobile app using Phonegap Build and Ionic. I am trying to make an XMLHttpRequest to a web service to get some XML data. The web service requires 3 parameters. I keep getting the following error:

ionic.bundle.js:26794 TypeError: Cannot read property 'open' of undefined.

Any ideas as to what I might be doing wrong?

I have attached the entire method below.

$scope.result = function callService(requestAction, requestXML){

  var httpObj = undefined; 

  if(window.XMLHttpRequest){    
    httpObj = new XMLHttpRequest();    
  }    
  else if (window.ActiveXObject){    
    httpObj = new ActiveXObject("Microsoft.XMLHTTP"); 
  }

  if(httpObj = undefined){
    alert("Failed creating Http Object");     
    return ""; 
  }

  if(requestAction == undefined || requestAction == null){
    requestAction = "";    
  }

  var async = false; 
  var url = "theurl";     
  var systemID = "thesystemid";     
  var requestAction = "GetEnquiry"; 
  var requestXML = "therequestxml"; 
  var params = "SystemID=" + systemID + "&RequestAction=" + requestAction + "&RequestXML=" + requestXML + "&OutputFormat=JSON";            
  var headers = "Content-type , application/x-www-form-urlencoded; charset=UTF-8"; 

  httpObj.open("POST", url, async);                 
  httpObj.send(params);

  if(httpObj.readyState == 4 && httpObj.status == 200){
    var result = httpObj.responseText; 
    console.log("This is the result: " + result);    
    return result; 
  }    
  else {    
    var result = httpObj.responseText;     
    return result; 
  }   
};   
})

Answer 1

The problem is the httpObj object which is undefined and you try to access a method on undefined . The reason why you don't show the error message (when httpObj is undefined ) you have defined in the alert is that you condition is not correct. This

if(httpObj = undefined){

should had been like below:

if(httpObj === undefined){

or equivalently like:

if(httObj){