index.php
Code:
<div style="position:fixed; left:300px; top: 500px; display:inline-block;"><strong><i><a href="#" id="previous" onClick="process('previous','<?=$postID?>')">Previous</a></i></strong></div>
getpost.js
Code:
var xmlHttp = createXmlHttpRequestObject();

function createXmlHttpRequestObject() {
    var xmlHttp;
    if(window.ActivexObject) {
        try{
            xmlHttp = new ActiveXObject("Microsoft.XMLHTTP");
        } catch(e) {
            xmlHttp = false;
        }
    } else {
        try {
            xmlHttp = new XMLHttpRequest();
        } catch(e) {
            xmlHttp = False;
        }
    }
    
    if(!xmlHttp)
        alert("XML Http Objhect cannot be created");
    
    else
        return xmlHttp;
}

function process(direction,$postID) {
    var direction = direction;
    var postID = $postID;
    
    if(xmlHttp.readyState==0 || xmlHttp.readystate==4) {//check if server is ready
        try{
            if (direction == 'previous') {
                xmlHttp.open("GET","getpost.php?postID="+postID+"&direction=previous", true);
            } else if (direction == 'next') {
                xmlHttp.open("GET","getpost.php?postID="+postID+"&direction=next", true);
            }
            xmlHttp.send('');
            //            xmlHttp.onreadystatechange = handleServerResponse;
            
            xmlHttp.onreadystatechange=function()
            {
                //                alert(xmlHttp.readyState + " " + xmlHttp.status);
                if (xmlHttp.readyState==4 && xmlHttp.status==200)
                {
                    xmlResponse = xmlHttp.responseXML;
                    xmlDocumentElement = xmlResponse.documentElement;
                    message = xmlDocumentElement.firstChild.data;
                    //document.getElementById("journalcontent").innerHTML = '<span style="color:blue">'+ message + '</span>';

                    var showElements = xmlResponse.getElementsByTagName("response");
                    //alert(showElements);//objectnodelist
                    
                    for (var x=0; x<showElements.length; x++) 
                    {
                        var journalID = showElements[x].childNodes[0].firstChild.data;
                        var title = showElements[x].childNodes[2].firstChild.data;                    
                        var content = showElements[x].childNodes[3].firstChild.data;                    
                        var datetime = showElements[x].childNodes[4].firstChild.data;
                        content = nl2br(content);
                        total = '<strong>' + title + '</strong><br /><br />' + content;
                        document.getElementById("journalcontent").innerHTML = total + '<div style="text-align:right;  border-bottom-width:2px; border-bottom-style:dashed; border-bottom-color:black;" id="datetime"></div>';
                        datetime = '<strong>' + datetime + '</strong>';
                        document.getElementById("datetime").innerHTML = datetime;
                        alert(journalID);
                        $('#previous').attr("onClick", "process('previous','"+ journalID + "')");
                    //                        document.getElementById("previous").onClick = "process('previous',<?="+ journalID + "?>)";
                    }
                    
//                    ajaxFinished = 1;
//                    
//                    //need to close the connection.
//                    xmlHttp = null;
                }
            }

        } catch(e) {
            alert(e.toString());
        }
    } else {
        setTimeout('process(direction,postID)', 1000)
    }
}

function nl2br (str, is_xhtml) {
    // http://kevin.vanzonneveld.net
    // +   original by: Kevin van Zonneveld (http://kevin.vanzonneveld.net)
    // +   improved by: Philip Peterson
    // +   improved by: Onno Marsman
    // +   improved by: Atli Þór
    // +   bugfixed by: Onno Marsman
    // +      input by: Brett Zamir (http://brett-zamir.me)
    // +   bugfixed by: Kevin van Zonneveld (http://kevin.vanzonneveld.net)
    // +   improved by: Brett Zamir (http://brett-zamir.me)
    // +   improved by: Maximusya
    // *     example 1: nl2br('Kevin\nvan\nZonneveld');
    // *     returns 1: 'Kevin<br />\nvan<br />\nZonneveld'
    // *     example 2: nl2br("\nOne\nTwo\n\nThree\n", false);
    // *     returns 2: '<br>\nOne<br>\nTwo<br>\n<br>\nThree<br>\n'
    // *     example 3: nl2br("\nOne\nTwo\n\nThree\n", true);
    // *     returns 3: '<br />\nOne<br />\nTwo<br />\n<br />\nThree<br />\n'
    var breakTag = (is_xhtml || typeof is_xhtml === 'undefined') ? '<br ' + '/>' : '<br>'; // Adjust comment to avoid issue on phpjs.org display

    return (str + '').replace(/([^>\r\n]?)(\r\n|\n\r|\r|\n)/g, '$1' + breakTag + '$2');
}
.

getpost.php works fine

I am able to click the button and get data back, but I am unable to get data back the second time I click the button.
Why?
I have also tried using the below 2
1.
// ajaxFinished = 1;

2.
// //need to close the connection.
// xmlHttp = null;