how to get only one value of returned data from ajax

Question

I have problem to get one value of returned data from ajax call to make a decision. this is my jquery code which call to a php file.

var displayMsg = $.ajax({
    url:"displayMessage.php"    
});
displayMsg.done(function(data){
    // I need to put an if condition in here.
})

this is my "displayMessage.php" file which takes its value from session

<?php 
session_start();
include "classes.php";
$chat = new chat();

$chat->setSenderUserName($_SESSION['userName']);
$chat->setReceiverUserName($_SESSION['receiverUserName']);
$chat->displayMessage();
?>

this file will call the function in the main file, and this is that function

public function displayMessage(){
    include "connection.php";
    $displayMsg = $connection->prepare("select date, senderUserName, message from messages where (senderUserName = ?
    and receiverUserName = ?) or (senderUserName = ? and receiverUserName = ?) order by date desc");
    $displayMsg->bind_param("ssss", $senderUserName, $receiverUserName, $receiverUserName, $senderUserName);

    $senderUserName=$this->getSenderUserName();
    $receiverUserName=$this->getReceiverUserName();

    $displayMsg->execute();
    $displayMsg->store_result();

    $displayMsg->bind_result($messageDate, $senderUserName, $message);
    while($displayMsg->fetch()){
        $this->setSenderUserName($senderUserName);
        $this->setMessage($message); 
        $this->setMessageDate($messageDate);
        ?>
        <span style="color:#00F"> <?php echo $this->getSenderUserName(); ?></span>&nbsp; says: <br />
        <?php echo $this->getMessage(); ?>
        <span class="date"><?php echo $this->getMessageDate(); ?></span><br />
        <?php
    }
}

now I want to access to messageDate value to compare it with the current time in successful part of ajax call (or in done part) but I don't know how. I try some solutions in site which was close to my case but none of them work and I receive Undefined or object Object. like:

$(data).find(".date").html();
$(data).find(".date").text();
$(data).find(".date").val();
$(date['date']);

Answer 1

if you are sure that displayMessage.php returns something in response use this code instead of your jquery code:

var displayMsg = null;
$.ajax({
url:"displayMessage.php",
success:function(data){
   displayMsg  = data;
       displayMsg.done(function(data){
       // I need to put an if condition in here.
       });
} 
});

be sure to check your condition inside success function because ajax may take long to response and jquery does not wait for it and continues to run next commands.