变量超出范围[重复]

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            <div class="grid--cell mb0 mt8">Closed <span title="2013-01-17 06:00:18Z" class="relativetime">7 years ago</span>.</div>
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Possible Duplicate:
How to return AJAX response Text?
How to return the response from an AJAX call from a function?

After whole day without solution to this. I read that this isn't possible or cant be done etc. I did go trough all of topics related, but cant find solution.

So i think my variable in code is out of scope and i cant return it, cant use it.

js file:

function getXMLHttp()
{
  var xmlHttp

  try
  {
    //Firefox, Opera 8.0+, Safari
    xmlHttp = new XMLHttpRequest();
  }
  catch(e)
  {
    //Internet Explorer
    try
    {
      xmlHttp = new ActiveXObject("Msxml2.XMLHTTP");
    }
    catch(e)
    {
      try
      {
        xmlHttp = new ActiveXObject("Microsoft.XMLHTTP");
      }
      catch(e)
      {
        alert("Your browser does not support AJAX!")
        return false;
      }
    }
  }
return xmlHttp;

}



function MakeRequest()
{
  var xmlHttp = getXMLHttp();

 xmlHttp.onreadystatechange = function(){


   if(xmlHttp.readyState == 4)
    {
      var myvar = new Array();
     myvar=JSON.parse(xmlHttp.responseText);

    return myvar;
    }





} 

   xmlHttp.open("GET", "showimage.php", true);
  xmlHttp.send();



}

So here above is ok, its returning value of php script when its finished.

And i want this myvar variable in html file. Tried like this:

 window.onload = function() {
 var myvar = MakeRequest();
 alert (myvar);

} 

It fails, returning undefined value.

Tried also making MakeRequest function as callback function, and then calling it from html like

MakeRequest(function(txt){
});

Then I got response, but can just alert it. I don't want to alert it. I need it to be stored in variable myvar because its needed later in code.

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