Get the base url using javascript

function getBaseURL() {
    var url = location.href;  // entire url including querystring - also: window.location.href;
    var baseURL = url.substring(0, url.indexOf('/', 14));
    if (baseURL.indexOf('http://localhost') != -1) {
        // Base Url for localhost
        var url = location.href;  // window.location.href;
        var pathname = location.pathname;  // window.location.pathname;
        var index1 = url.indexOf(pathname);
        var index2 = url.indexOf("/", index1 + 1);
        var baseLocalUrl = url.substr(0, index2);
        return baseLocalUrl + "/";
    }
    else {
        // Root Url for domain name
        return baseURL + "/";
    }

} 

session logoff using javascript

 var timer;
    document.onkeypress=resetTimer;
    document.onmousemove=resetTimer;
    function resetTimer()
    {
        clearTimeout(timer);
        var sessionTimeSpan='<%=ConfigurationManager.AppSettings["sessionTimeOut"].ToString() %>';
//session timespan in minutes
        timer=setTimeout("logout()", 60000*sessionTimeSpan);
    }

    function logout()
    {
        alert('Session timed out. Please login again.');
       window.location.href=window.location.protocol+'//'+window.location.hostname+ '/Login.aspx';
//To get the base url
var baseUrl=getBaseURL();
       window.location.href=baseUrl+ 'Login.aspx';
    }