js get ifrme subpages execution order value problem

Parent page code is as follows
js code :
function pTest () {
var url = "child.jsp";
$ ("# mainFrame"). attr ("src", url);

var msg = document.mainFrame.resultStr ;/ / this is to get a js subpages string variable
}
html:

subpages as follows:

body has a
initDeptData () {
$. ajax ({
type: "POST",
url: url,
data: "", / / ​​submit the entire form
success: function (msg) {

/ / there is return a string through the business process
resultStr = msg;

},
error: function () {
alert (' Error initializing sector information ! ' ) ;
}
});
}

questions are as follows , I want to get the parent page document.mainFrame.resultStr, but there is a problem, because subpages initDeptData () This method will consume some time, I now want when resultStr = msg ; to return immediately when this msg to acquire document.mainFrame.resultStr, how to do ? ? ?
I am now using setTimeout, but this is not insurance , it may result in a waste of time

solved ....




------ Solution ------------------------------------ --------
You can call the parent page subpages js method, and then put the string passed over. Should be. . .
------ Solution ---------------------------------------- ----
subpages parent page in variable assignment
------ Solution ------------------------- -------------------
example, you define subpages

<script>
  var zipphone = "<?= $phone ?>";
   </script>

parent page you can define such a method values:

function zipPhoneCallback(zipphone) {
      ((console&&console.log)||alert)("zipphone = " + zipphone);
  }

Then subpages pass this value:

window.parent.zipPhoneCallback(zipphone);

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moment did not turn around , you're on it ....
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and second floor almost, thank
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has been resolved, with Frank