background.js

var count;
var fetching = false;
chrome.browserAction.onClicked.addListener(function(a) {
    chrome.tabs.create({'url' : 'http://www.v2ex.com/notifications'});
});
function fetchNotify() {
    if(!fetching) {
        fetching = true;
        $.get("http://www.v2ex.com/faq", function(r) {
            count = r.match(/<title>V2EX \((.*)\)<\/title>/);
            if(count !== null) {
                chrome.browserAction.setBadgeText({
                    'text' : r.match(/<title>V2EX \((.*)\)<\/title>/)[1]
                });
            }else{
                chrome.browserAction.setBadgeText({'text' : ''});
            }
            fetching = false;
        });
    }
}
fetchNotify();
setInterval(fetchNotify, 120000);