Doubt in Ajax: get responseText in main function

[shiniskumar]

i go tto perform some validation while ck=liking a button without refreshing the value.. i used ajax.My code is as follows...on button click i call the function validateGridAdd();
Inside tat function i need to call the function tat uses ajax to go to the server and come back.. the resultant value is to be obtained in the main function validateGridAdd().

//main function
function validateGridAdd(a,rowNum){
    var tForm = document.hallAllotFrm;
        if(!validateCommon()){
            return;
        }
 
        getValidation();    
    var length = document.getElementsByName("arrInv").length; 
        var invArr = document.getElementsByName("arrInv");
        var currInv = document.getElementById("arrInv0");
        var currRel = document.getElementById("arrReliev3");
 
        if(currInv.value==currRel.value){
            alert('Supervisor and  Relieving Faculty cannot be same person.');
            return false;
        }
 
        return true;
    } 
 
//function for ajax
function getValidation(){
 
var tForm = document.hallAllotFrm;
 
        var invig = document.getElementById("arrInv0").value;
        var fromTime = document.getElementById("arrFrom1").value;
        var toTime = document.getElementById("arrTo2").value;
        var examDate = document.getElementById("date").value;
 
        var url = "validateSchedule.action?invigId=" + invig+""+'&fromTime='+fromTime
         +""+'&toTime='+toTime+""+'&examDate='+examDate+""+'&flag='+flag;
 
 populateSelectBoxes(url);
 
}
 
function populateSelectBoxes(url){ 
 
        if (window.XMLHttpRequest) {
                req = new XMLHttpRequest();
        } else if (window.ActiveXObject) {
          req = new ActiveXObject("Microsoft.XMLHTTP");
        }                                               
        req.open("GET", url, true);
        req.onreadystatechange = populateTextField;
        req.setRequestHeader('Accept','message/x-jl-formresult');
        req.send(null);  
}
 
function populateTextField(){   
    if (req.readyState == 4 && req.status == 200) {                 
                 value=req.responseText;
             if(value=="true"){
                alert("Supervisor scheduled for class.Please select another supervisor");
                  document.getElementById("arrInv0").value=-1;
                 } 
       }
document.getElementById("flag").value=value;
    } 

ive got a hidden variable "flag" in my code.. tat variable is set to the responseText in my function. i need to get the responseText in my main function validateGridAdd(a,rowNum);
the value of flag can be eithr true or false.
How do i get this value in the main function.?

[acoder]

Once you've set the flag, it should be available in the main function though with the asynchronous nature of things, the question is when. The best thing would be to just put the code that depends on this variable setting in populateTextField().