error: function not defined. new to javascript and need help!

I am writing an app that displays content from an RSS feed. I got the code to start it off from a sample on the Web and I am modifying it. However the sample uses “prototype” and I have no idea how to add on to this. My latest error is trying to add a function called “next()” which will display the next RSS item. My browser is saying “next() is not defined” when I try to call next().

Here is my javascript for the next() function:

[CODE]
// ————————————————————–
// next() – Displays the next article
// ————————————————————–
rss_browser.prototype.next=function(){
this.rotatemsg();
}
[/CODE]

Here is my whole program which contains next() and rotatemsg().
Apologies for not being more specific, but I’m a newb and might miss including something important if I leave some code out.

[CODE]
function createAjaxObj(){
var httprequest=false
if (window.XMLHttpRequest){ // if Mozilla, Safari etc
httprequest=new XMLHttpRequest()
if (httprequest.overrideMimeType)
httprequest.overrideMimeType(‘text/xml’);
}
else if (window.ActiveXObject){ // if IE
try {
httprequest=new ActiveXObject(“Msxml2.XMLHTTP”);
}
catch (e){
try{
httprequest=new ActiveXObject(“Microsoft.XMLHTTP”);
}
catch (e){}
}
}
return httprequest;
}

// ——————————————————————-
// Main RSS Ticker Object function
// rss_browser(RSS_id, cachetime, divId, divClass, optionalswitch)
// ——————————————————————-

function rss_browser(RSS_id, cachetime, divId, divClass, optionalswitch){
this.RSS_id=RSS_id; //Array key indicating which RSS feed to display
this.cachetime=cachetime; //Time to cache feed, in minutes. 0=no cache.
this.tickerid=divId; //ID of ticker div to display information
this.logicswitch=(typeof optionalswitch!=”undefined”)? optionalswitch : -1;
this.pointer = 0;
this.ajaxobj=createAjaxObj();
document.write(‘<div id=”‘+divId+'” class=”‘+divClass+'”>Initializing ticker…</div>’);
this.getAjaxcontent();
}

// ——————————————————————-
// getAjaxcontent()- Makes asynchronous GET request to “rssfetch.php” with the supplied parameters
// ——————————————————————-

rss_browser.prototype.getAjaxcontent=function(){
if (this.ajaxobj){
var instanceOfTicker=this;
var parameters=”id=”+encodeURIComponent(this.RSS_id)+”&cachetime=”+this.cachetime+”&bustcache=”+new Date().getTime();
this.ajaxobj.onreadystatechange=function(){instanceOfTicker.initialize()};
this.ajaxobj.open(‘GET’, “retrieveRSS.php?”+parameters, true);
this.ajaxobj.send(null);
}
}

// ——————————————————————-
// initialize()- Initialize ticker method.
// -Gets contents of RSS content and parse it using JavaScript DOM methods
// ——————————————————————-

rss_browser.prototype.initialize=function(){
if (this.ajaxobj.readyState == 4){ //if request of file completed
if (this.ajaxobj.status==200){ //if request was successful
var xmldata=this.ajaxobj.responseXML;
if (xmldata.getElementsByTagName(“item”).length==0){ //if no <item> elements found in returned content
document.getElementById(this.tickerid).innerHTML=”<b>Error</b> fetching remote RSS feed!<br />”+this.ajaxobj.responseText;
return;
}
var instanceOfTicker=this;
this.feeditems=xmldata.getElementsByTagName(“item”);

//Cycle through RSS XML object and store each piece of the item element as an attribute of the element
for (var i=0; i<this.feeditems.length; i++){
this.feeditems[i].setAttribute(“ctitle”, this.feeditems[i].getElementsByTagName(“title”)[0].firstChild.nodeValue);
this.feeditems[i].setAttribute(“clink”, this.feeditems[i].getElementsByTagName(“link”)[0].firstChild.nodeValue);
this.feeditems[i].setAttribute(“cdescription”, this.feeditems[i].getElementsByTagName(“description”)[0].firstChild.nodeValue);
}
document.getElementById(this.tickerid).onmouseover=function(){instanceOfTicker.mouseoverBol=1};
document.getElementById(this.tickerid).onmouseout=function(){instanceOfTicker.mouseoverBol=0};
this.rotatemsg();
}
}
}

// ——————————————————————-
// rotatemsg()- Rotate through RSS messages and displays them
// ——————————————————————-

rss_browser.prototype.rotatemsg=function(){
var instanceOfTicker=this;
var tickerDiv=document.getElementById(this.tickerid);
var tickercontent='<a href=”‘+this.feeditems[this.pointer].getAttribute(“clink”)+'”>’+this.feeditems[this.pointer].getAttribute(“ctitle”)+'</a>’;
if (this.logicswitch==”showdescription”)
tickercontent+=”<br />”+this.feeditems[this.pointer].getAttribute(“cdescription”);
tickerDiv.innerHTML=tickercontent;
this.pointer=(this.pointer<this.feeditems.length-1)? this.pointer+1 : 0;
}

// ————————————————————–
// previous() – Displays the previous article
// ————————————————————–
function previous(){
alert(“previous clicked!”);
}

// ————————————————————–
// next() – Displays the next article
// ————————————————————–
rss_browser.prototype.next=function(){
this.rotatemsg();
}
[/CODE]

Please help! Thank you.

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