https://www.midwestclinic.org/js/timer.js

1//Dim sLoadString As String = "window.setTimeout(""window.location.href='" & ConfigurationManager.AppSettings("WebRoot") & "session_timeout.html'""," & (Session.Timeout * 60 * 1000) + 10000 & ");"
2
3var sessionstartTimeMS = 0;  // EPOCH Time of event count started
4var sessiontimerId;          // Current timer handler
5var sessiontimerStep = 0;   // Time beetwen calls
6var sessiontimerWarningStep = 0;
7var sessiontimerWarningID;
8
9// This function starts the timer
10function startTimer(timerLength, timerWarning) {
11    sessionstartTimeMS = (new Date()).getTime();
12    sessiontimerStep = timerLength;
13    sessiontimerWarningStep = timerWarning;
14    //alert('Began');
15    sessiontimerWarningID = window.setTimeout(showWarning, sessiontimerWarningStep); 
16    sessiontimerId = window.setTimeout(redirectPage, sessiontimerStep);
17}
18
19// This function raises the event when the time has reached and
20// Starts a new timer to execute the opeartio again in the defined time
21function redirectPage() {
22
23    //alert('WOP EVENT RAISED!');
24
25    clearTimeout(sessiontimerId); // clear timer
26    clearTimeout(sessiontimerWarningID); 
27    //startTimer(sessiontimerStep); // do again
28    //window.location.href = 'session-timeout.aspx';
29    window.location.href = '/login?logout=true&session=true';
30}
31
32// Gets the number of ms remaining to execute the eventRaised Function
33function getRemainingTime() {
34    return sessiontimerStep - ((new Date()).getTime() - sessionstartTimeMS);
35}
36
37//function showWarning() {
38//    alert('Not alot of time left');
39//}
40
41function showWarning() {
42    var div = document.getElementById('divWarning');
43    try {
44        div.style.visibility = 'visible';
45        div.style.display = 'block';
46    }
47    catch (Error) {
48    }
49    try {
50        div.setAttribute('style', 'display: block; visibility: visible');
51
52    }
53    catch (Error) {
54    }
55    try { }
56    catch (Error) {
57    }
58    window.location.href = '#';
59}
60
61function hideWarning(divName) {
62    var div = document.getElementById(divName);
63    try {
64        div.style.visibility = 'hidden';
65        div.style.display = 'none';
66    }
67    catch (Error) {
68    }
69    try {
70        div.setAttribute('style', 'display: none; visibility: hidden');
71
72    }
73    catch (Error) {
74    }
75    try { }
76    catch (Error) {
77    }
78}