ASP.NET Forum

**Sleeping Troll** · 06-09-2008, 04:25 PM

Code:

 
<script>
 
var OrderData
 
<!--
 
function GetOrder(){
try
 {
 xmlHttp=new ActiveXObject("Msxml2.XMLHTTP");    
 }
catch (e)
  {
  try
   {      
   xmlHttp=new ActiveXObject("Microsoft.XMLHTTP");      
   }
    catch (e)
      {      
    alert("Your browser is not supported");
    return false;
    }    
  }  
   xmlHttp.onreadystatechange=function()
    {
    if(xmlHttp.readyState==4)
    {
     OrderData=xmlHttp.responseText;
     alert(OrderData)//This alert returns values
  }
  }
 var ReqString = "CustID="+CustID;
  xmlHttp.open("GET","GetItems.asp?"+ReqString,true);
 xmlHttp.send(null);
}
 
 
function Init()
{
OrderData=GetOrder()
}
alert(OrderData)//This alert returns "undefined"
-->
</script>

HTML Code:

</head>
<body onLoad="Init();">

**chrishirst** · 06-09-2008, 06:48 PM

Quote:

function Init()
{
OrderData=GetOrder()
}
alert(OrderData)//This alert returns "undefined"

Well it would, seeing as how you set the value of OrderData to be a function NOT the value from the function. Because the function does NOT return a value.

you are missing the return xmlHttp.responseText; from the AJAX call

Your code is a bit of a mish mash in rather poor VB style code by trying to use a global scoped variable to pass values instead of allowing the function to actually return a value.

javascript & JScript are rather less forgiving on sloppy code than VB/VBScript is.

to use the code syntax you had, the Init() call should be

Code:

function Init()
{
GetOrder()
alert(OrderData)
}

Using a globally scoped variable for passing values between sub / function calls is poor practice and will lead to more and more problems as your application grows.
If you need a global value, define as a read only property, it is much safer if your code cannot accidentally redefine it or overwrite the value.

**Sleeping Troll** · 07:12 PM

All good advice Chris, however I originally used the return and the syntax:
function Init()
{
GetOrder()
alert(OrderData)
}

same result. Your advice on Global variables is good, but(notice I referred to my thesaurus to avoid using however again!) There are 10 variables that are common to most pages in my site and I am passing them via querystring. In the case of OrderData, by the by(nevermind) I am using a global variable out of pure desperation! As a global variable I cannot understand how one alert sees it and the other doesn't? Any ideas?

P.S. Really impressed by your ability to interpret code!

**nyef** · 06-09-2008, 07:21 PM

The ajax call is asynchronous. When you call GetOrder(), it may take a second or two for it to get the results. When you call alert(OrderData) (which should be INSIDE the init function btw) immediately after calling GetOrder, OrderData still hasn't been defined (and won't be for another second or two).

You can initiate a loop and wait for OrderData to be populated:

Code:

for (var haveData=false;!haveData;haveData=(typeof(OrderData)!='undefined')));

Or you could just move the order processing code to inside the onreadystatechange function.

**Sleeping Troll** · 07:39 PM

By George, I think you have it! Thank you, Thank you very much!

Arrrgh! the first alert does not occur until the readystate change test = 4!

If the cause was async both alerts would return "undefined", this is really perplexing how is it possible that 2 alerts on the same page can see a global differently?

**nyef** · 06-12-2008, 12:10 AM

He's right, you need to change OrderData=GetOrder() to just GetOrder() (drop the "OrderData=")...

The way you have it now, when you call GetOrder(), it executes the call for the xmlhttp, then sets OrderData to be the results. But then in the Init() function, right after GetOrder() is called, the variables OrderData is set AGAIN to be the return value of the GetOrder() function. Since that return value was never specified, it is setting the OrderData variable twice, once inside the GetOrder() function to the results of the http call, then again outside the GetOrder() function but inside the Init() function, it sets it to 'undefined' the second time since there is no return call.