当另一个客户端点击提交时,在一个客户端上显示一个弹出窗口

Sorry, I'm new here so please forgive any bad formatting :)

I want that when the delegate from delegate.php types something in their input field and click submit, a pop up window will appear on chair's page containing the content of delegate's input field.

I've tried using AJAX but it doesn't seem to work, any help is much appreciated. I have attached delegate.php and chair.php here

delegate.php

    <html>
    <head>
    <script src = "jquery-1.11.3.min.js"/>
    <script type="text/javascript">
    function validate()
    {
        var xmlhttp;
        if(window.XMLHttpRequest)
    {
        xmlhttp=new XMLHttpRequest();
    }
    else
    {
       xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
    }

    xmlhttp.onreadystatechange=function()
    {
       if(xmlhttp.readystate==4 && xmlhttp.status==200)
       {
     document.getElementById("textContent").innerHTML=xmlhttp.responseText;
       }
    };
    a = document.getElementById("textContent").value;
    alert(a);
    xmlhttp.open("GET", "temp.php?="+a, true);
    xmlhttp.send();
    }

    </script>
    <title>Delegate Page </title>
    <h1> Welcome Delegate </h1>
    </head>

    <form>
    <input type="text" name="contents" id="textContent" name="text">
    <input type="submit" onclick="validate();">
    </form>
    </html>

chair.php

    <?php
    $text = $_GET['textContent'];
    print '<h1>'.$text.'<h1>';
    ?>