I need to scrape some pages, the problem is that some of these pages are using javascript to load part of their contexts and some not! and there is no common tag or content to determine if context loaded! also I can't use timer or loop to wait and check if context changed! Currently I'm using web-browser to scrape and pars the context.
I'm already using following code to check if page completely loaded and check if page content is changed but it's not work properly.
while (wb.ReadyState != System.Windows.Forms.WebBrowserReadyState.Complete)
{
System.Windows.Forms.Application.DoEvents();
}
Any idea how tackle this? Thanks.
I hope the following code will help you
Create a function method to wait for a few seconds
public void Wait(int sec)
{
System.Windows.Forms.Timer timer1 = new System.Windows.Forms.Timer();
if (sec == 0 || sec < 0) return;
timer1.Interval = sec * 1000;
timer1.Enabled = true;
timer1.Start();
timer1.Tick += (s, e) =>
{
timer1.Enabled = false;
timer1.Stop();
};
while (timer1.Enabled)
{
Application.DoEvents();
}
}
Write the following code in the DocumentCompleted event. Check the element has value or null if null wait for 2 sec and continue this process 30 times, nearly one minute. If it is not loaded display a message like a page not loaded
int cnt = 0;
HtmlElement htmlElement = WebBrowser1.Document.GetElementById("elementID")
do
{
Wait(2);
cnt++;
htmlElement = WebBrowser1.Document.GetElementById("elementID")
if (cnt > 30)
{
throw new Exception();
}
} while (htmlElement == null);
If scraping using a browser works, then try using PuppeteerSharp, which is a "Headless Chrome .NET API".
You should be able to do the same thing entirely in C#.
I have a PhantomJS script that I'm trying to use in order to essentially generate a video of a particular website.
var page = require('webpage').create();
page.viewportSize = {
width: 1280,
height: 720
};
page.open('http://my-awesome-site.whatever', function() {
var fps = 30;
var seconds = 10;
var elapsed = 0;
var current = 0;
takeScreenShot();
function takeScreenShot() {
if (elapsed < seconds * 1000) {
page.render('screenshot_' + (current++) + '.png');
elapsed += 1000 / fps;
setTimeout(takeScreenShot, 1000 / fps);
}
else {
phantom.exit();
}
}
});
The above script will attempt to take 30 screenshots per second for 10 seconds, which I then combine into an mp4 using ffmpeg.
The problem is that the page.render() function is not instantaneous, and does not halt the scripts running on the page. So when I'm pointing at a page using jQuery animations, which I believe rely on setTimeout, those timeouts continue to run while each screenshot is processed. As a result, the outputted video appears greatly sped up.
Is there a way through PhantomJS to pause script execution? What I'm hoping for is to do something like:
page.pause();
page.render('screenshot_' + (current++) + '.png');
page.resume();
But sadly, I don't see anything like that in their api docs.
You could set page.settings.javascriptEnabled=false if the page looks don't depend on JS too much.
Be aware that you need to define the settings before the first call as they are evaluated only once eg :
var page = require('webpage').create();
page.settings = {
javascriptEnabled=false
}
See : http://phantomjs.org/api/webpage/property/settings.html
If it doesn't fit your need, you need to dig into the code of the page to find a way to stop the animations (use your browser's console). Once you know what you need to do, just evaluate the command in Phantom.
page.open('http://my-awesome-site.whatever', function() {
var stopScripts = page.evaluate(function() {
// do whatever you need to stop execution
return true;
});
// ... take your screenshots
});
This is what i have. My problem is, each loop doesn't wait setTimeout to complete its job. I have 2 console.log('elmDuration = ')... before slider.goToNextSlide executed. Which is wrong. I would use generator functions and yield if this is a server side code, but not.
$('li').each(function(index, elm){
var image = $(elm).find('img')[0];
var video = $(elm).find('video')[0];
var media = image || video;
var elmDuration = $(media).attr('data-duration');
console.log("elmDuration = ", elmDuration);
(function(){
setTimeout(slider.goToNextSlide, elmDuration * 1000);
})();
});
I am stuck with this. Thanks.
If you want to advance to the next element when the timeout finished, you have to do that manually:
var $lis = $('li');
var index = 0;
function next(index) {
var elem = $lis[index];
var image = $(elm).find('img')[0];
var video = $(elm).find('video')[0];
var media = image || video;
// if there is always going to be either an img **or** a video element,
// you can directly do
// var elmDuration = $(elem).find('img, video').attr('data-duration');
var elmDuration = $(media).attr('data-duration');
console.log("elmDuration = ", elmDuration);
setTimeout(function() {
slider.goToNextSlide();
if (index < ($lis.length - 1)) {
next(++index);
}
}, elmDuration * 1000);
}
next(index);
each loop is not going to wait for setTimeout. It will execute for all elements in $('li') before setTimeouts start firing. The purpose of setTimeout is to let the code that calls it proceed without interruption and execute the first parameter when timeout occurs.
You have to take the code out of the setTimeout if you want it to execute inside the loop. SetTimeout is a way to execute code in x milliseconds, but it won't execute until the single javascript thread is available. The loop will keep the thread busy, so all the seTimeouts will have to wait until the end.
I have a button which runs a long running function when it's clicked. Now, while the function is running, I want to change the button text, but I'm having problems in some browsers like Firefox, IE.
html:
<button id="mybutt" class="buttonEnabled" onclick="longrunningfunction();"><span id="myspan">do some work</span></button>
javascript:
function longrunningfunction() {
document.getElementById("myspan").innerHTML = "doing some work";
document.getElementById("mybutt").disabled = true;
document.getElementById("mybutt").className = "buttonDisabled";
//long running task here
document.getElementById("myspan").innerHTML = "done";
}
Now this has problems in firefox and IE, ( in chrome it works ok )
So I thought to put it into a settimeout:
function longrunningfunction() {
document.getElementById("myspan").innerHTML = "doing some work";
document.getElementById("mybutt").disabled = true;
document.getElementById("mybutt").className = "buttonDisabled";
setTimeout(function() {
//long running task here
document.getElementById("myspan").innerHTML = "done";
}, 0);
}
but this doesn't work either for firefox! the button gets disabled, changes colour ( due to the application of the new css ) but the text does not change.
I have to set the time to 50ms instead of just 0ms, in order to make it work ( change the button text ). Now I find this stupid at least. I can understand if it would work with just a 0ms delay, but what would happen in a slower computer? maybe firefox would need 100ms there in the settimeout? it sounds rather stupid. I tried many times, 1ms, 10ms, 20ms...no it won't refresh it. only with 50ms.
So I followed the advice in this topic:
Forcing a DOM refresh in Internet explorer after javascript dom manipulation
so I tried:
function longrunningfunction() {
document.getElementById("myspan").innerHTML = "doing some work";
var a = document.getElementById("mybutt").offsetTop; //force refresh
//long running task here
document.getElementById("myspan").innerHTML = "done";
}
but it doesn't work ( FIREFOX 21). Then i tried:
function longrunningfunction() {
document.getElementById("myspan").innerHTML = "doing some work";
document.getElementById("mybutt").disabled = true;
document.getElementById("mybutt").className = "buttonDisabled";
var a = document.getElementById("mybutt").offsetTop; //force refresh
var b = document.getElementById("myspan").offsetTop; //force refresh
var c = document.getElementById("mybutt").clientHeight; //force refresh
var d = document.getElementById("myspan").clientHeight; //force refresh
setTimeout(function() {
//long running task here
document.getElementById("myspan").innerHTML = "done";
}, 0);
}
I even tried clientHeight instead of offsetTop but nothing. the DOM does not get refreshed.
Can someone offer a reliable solution preferrably non-hacky ?
thanks in advance!
as suggested here i also tried
$('#parentOfElementToBeRedrawn').hide().show();
to no avail
Force DOM redraw/refresh on Chrome/Mac
TL;DR:
looking for a RELIABLE cross-browser method to have a forced DOM refresh WITHOUT the use of setTimeout (preferred solution due to different time intervals needed depending on the type of long running code, browser, computer speed and setTimeout requires anywhere from 50 to 100ms depending on situation)
jsfiddle: http://jsfiddle.net/WsmUh/5/
Webpages are updated based on a single thread controller, and half the browsers don't update the DOM or styling until your JS execution halts, giving computational control back to the browser. That means if you set some element.style.[...] = ... it won't kick in until your code finishes running (either completely, or because the browser sees you're doing something that lets it intercept processing for a few ms).
You have two problems: 1) your button has a <span> in it. Remove that, just set .innerHTML on the button itself. But this isn't the real problem of course. 2) you're running very long operations, and you should think very hard about why, and after answering the why, how:
If you're running a long computational job, cut it up into timeout callbacks (or, in 2019, await/async - see note at the end of this anser). Your examples don't show what your "long job" actually is (a spin loop doesn't count) but you have several options depending on the browsers you take, with one GIANT booknote: don't run long jobs in JavaScript, period. JavaScript is a single threaded environment by specification, so any operation you want to do should be able to complete in milliseconds. If it can't, you're literally doing something wrong.
If you need to calculate difficult things, offload it to the server with an AJAX operation (universal across browsers, often giving you a) faster processing for that operation and b) a good 30 seconds of time that you can asynchronously not-wait for the result to be returned) or use a webworker background thread (very much NOT universal).
If your calculation takes long but not absurdly so, refactor your code so that you perform parts, with timeout breathing space:
function doLongCalculation(callbackFunction) {
var partialResult = {};
// part of the work, filling partialResult
setTimeout(function(){ doSecondBit(partialResult, callbackFunction); }, 10);
}
function doSecondBit(partialResult, callbackFunction) {
// more 'part of the work', filling partialResult
setTimeout(function(){ finishUp(partialResult, callbackFunction); }, 10);
}
function finishUp(partialResult, callbackFunction) {
var result;
// do last bits, forming final result
callbackFunction(result);
}
A long calculation can almost always be refactored into several steps, either because you're performing several steps, or because you're running the same computation a million times, and can cut it up into batches. If you have (exaggerated) this:
var resuls = [];
for(var i=0; i<1000000; i++) {
// computation is performed here
if(...) results.push(...);
}
then you can trivially cut this up into a timeout-relaxed function with a callback
function runBatch(start, end, terminal, results, callback) {
var i;
for(var i=start; i<end; i++) {
// computation is performed here
if(...) results.push(...); }
if(i>=terminal) {
callback(results);
} else {
var inc = end-start;
setTimeout(function() {
runBatch(start+inc, end+inc, terminal, results, callback);
},10);
}
}
function dealWithResults(results) {
...
}
function doLongComputation() {
runBatch(0,1000,1000000,[],dealWithResults);
}
TL;DR: don't run long computations, but if you have to, make the server do the work for you and just use an asynchronous AJAX call. The server can do the work faster, and your page won't block.
The JS examples of how to deal with long computations in JS at the client are only here to explain how you might deal with this problem if you don't have the option to do AJAX calls, which 99.99% of the time will not be the case.
edit
also note that your bounty description is a classic case of The XY problem
2019 edit
In modern JS the await/async concept vastly improves upon timeout callbacks, so use those instead. Any await lets the browser know that it can safely run scheduled updates, so you write your code in a "structured as if it's synchronous" way, but you mark your functions as async, and then you await their output them whenever you call them:
async doLongCalculation() {
let firstbit = await doFirstBit();
let secondbit = await doSecondBit(firstbit);
let result = await finishUp(secondbit);
return result;
}
async doFirstBit() {
//...
}
async doSecondBit...
...
SOLVED IT!! No setTimeout()!!!
Tested in Chrome 27.0.1453, Firefox 21.0, Internet 9.0.8112
$("#btn").on("mousedown",function(){
$('#btn').html('working');}).on('mouseup', longFunc);
function longFunc(){
//Do your long running work here...
for (i = 1; i<1003332300; i++) {}
//And on finish....
$('#btn').html('done');
}
DEMO HERE!
As of 2019 one uses double requesAnimationFrame to skip a frame instead of creating a race condition using setTimeout.
function doRun() {
document.getElementById('app').innerHTML = 'Processing JS...';
requestAnimationFrame(() =>
requestAnimationFrame(function(){
//blocks render
confirm('Heavy load done')
document.getElementById('app').innerHTML = 'Processing JS... done';
}))
}
doRun()
<div id="app"></div>
As an usage example think of calculating pi using Monte Carlo in an endless loop:
using for loop to mock while(true) - as this breaks the page
function* piMonteCarlo(r = 5, yield_cycle = 10000){
let total = 0, hits = 0, x=0, y=0, rsqrd = Math.pow(r, 2);
while(true){
total++;
if(total === Number.MAX_SAFE_INTEGER){
break;
}
x = Math.random() * r * 2 - r;
y = Math.random() * r * 2 - r;
(Math.pow(x,2) + Math.pow(y,2) < rsqrd) && hits++;
if(total % yield_cycle === 0){
yield 4 * hits / total
}
}
}
let pi_gen = piMonteCarlo(5, 1000), pi = 3;
for(let i = 0; i < 1000; i++){
// mocks
// while(true){
// basically last value will be rendered only
pi = pi_gen.next().value
console.log(pi)
document.getElementById('app').innerHTML = "PI: " + pi
}
<div id="app"></div>
And now think about using requestAnimationFrame for updates in between ;)
function* piMonteCarlo(r = 5, yield_cycle = 10000){
let total = 0, hits = 0, x=0, y=0, rsqrd = Math.pow(r, 2);
while(true){
total++;
if(total === Number.MAX_SAFE_INTEGER){
break;
}
x = Math.random() * r * 2 - r;
y = Math.random() * r * 2 - r;
(Math.pow(x,2) + Math.pow(y,2) < rsqrd) && hits++;
if(total % yield_cycle === 0){
yield 4 * hits / total
}
}
}
let pi_gen = piMonteCarlo(5, 1000), pi = 3;
function rAFLoop(calculate){
return new Promise(resolve => {
requestAnimationFrame( () => {
requestAnimationFrame(() => {
typeof calculate === "function" && calculate()
resolve()
})
})
})
}
let stopped = false
async function piDOM(){
while(stopped==false){
await rAFLoop(() => {
pi = pi_gen.next().value
console.log(pi)
document.getElementById('app').innerHTML = "PI: " + pi
})
}
}
function stop(){
stopped = true;
}
function start(){
if(stopped){
stopped = false
piDOM()
}
}
piDOM()
<div id="app"></div>
<button onclick="stop()">Stop</button>
<button onclick="start()">start</button>
As described in the "Script taking too long and heavy jobs" section of Events and timing in-depth (an interesting reading, by the way):
[...] split the job into parts which get scheduled after each other. [...] Then there is a “free time” for the browser to respond between parts. It is can render and react on other events. Both the visitor and the browser are happy.
I am sure that there are many times in which a task cannot be splitted into smaller tasks, or fragments. But I am sure that there will be many other times in which this is possible too! :-)
Some refactoring is needed in the example provided. You could create a function to do a piece of the work you have to do. It could begin like this:
function doHeavyWork(start) {
var total = 1000000000;
var fragment = 1000000;
var end = start + fragment;
// Do heavy work
for (var i = start; i < end; i++) {
//
}
Once the work is finished, function should determine if next work piece must be done, or if execution has finished:
if (end == total) {
// If we reached the end, stop and change status
document.getElementById("btn").innerHTML = "done!";
} else {
// Otherwise, process next fragment
setTimeout(function() {
doHeavyWork(end);
}, 0);
}
}
Your main dowork() function would be like this:
function dowork() {
// Set "working" status
document.getElementById("btn").innerHTML = "working";
// Start heavy process
doHeavyWork(0);
}
Full working code at http://jsfiddle.net/WsmUh/19/ (seems to behave gently on Firefox).
If you don't want to use setTimeout then you are left with WebWorker - this will require HTML5 enabled browsers however.
This is one way you can use them -
Define your HTML and an inline script (you don't have to use inline script, you can just as well give an url to an existing separate JS file):
<input id="start" type="button" value="Start" />
<div id="status">Preparing worker...</div>
<script type="javascript/worker">
postMessage('Worker is ready...');
onmessage = function(e) {
if (e.data === 'start') {
//simulate heavy work..
var max = 500000000;
for (var i = 0; i < max; i++) {
if ((i % 100000) === 0) postMessage('Progress: ' + (i / max * 100).toFixed(0) + '%');
}
postMessage('Done!');
}
};
</script>
For the inline script we mark it with type javascript/worker.
In the regular Javascript file -
The function that converts the inline script to a Blob-url that can be passed to a WebWorker. Note that this might note work in IE and you will have to use a regular file:
function getInlineJS() {
var js = document.querySelector('[type="javascript/worker"]').textContent;
var blob = new Blob([js], {
"type": "text\/plain"
});
return URL.createObjectURL(blob);
}
Setup worker:
var ww = new Worker(getInlineJS());
Receive messages (or commands) from the WebWorker:
ww.onmessage = function (e) {
var msg = e.data;
document.getElementById('status').innerHTML = msg;
if (msg === 'Done!') {
alert('Next');
}
};
We kick off with a button-click in this demo:
document.getElementById('start').addEventListener('click', start, false);
function start() {
ww.postMessage('start');
}
Working example here:
http://jsfiddle.net/AbdiasSoftware/Ls4XJ/
As you can see the user-interface is updated (with progress in this example) even if we're using a busy-loop on the worker. This was tested with an Atom based (slow) computer.
If you don't want or can't use WebWorker you have to use setTimeout.
This is because this is the only way (beside from setInterval) that allow you to queue up an event. As you noticed you will need to give it a few milliseconds as this will give the UI engine "room to breeth" so-to-speak. As JS is single-threaded you cannot queue up events other ways (requestAnimationFrame will not work well in this context).
Hope this helps.
Update: I don't think in the long term that you can be sure of avoiding Firefox's aggressive avoidance of DOM updates without using a timeout. If you want to force a redraw / DOM update, there are tricks available, like adjusting the offset of elements, or doing hide() then show(), etc., but there is nothing very pretty available, and after a while when those tricks get abused and slow down user experience, then browsers get updated to ignore those tricks. See this article and the linked articles beside it for some examples: Force DOM redraw/refresh on Chrome/Mac
The other answers look like they have the basic elements needed, but I thought it would be worthwhile to mention that my practice is to wrap all interactive DOM-changing functions in a "dispatch" function which handles the necessary pauses needed to get around the fact that Firefox is extremely aggressive in avoiding DOM updates in order to score well on benchmarks (and to be responsive to users while browsing the internet).
I looked at your JSFiddle and customized a dispatch function the one that many of my programs rely on. I think it is self-explanatory, and you can just paste it into your existing JS Fiddle to see how it works:
$("#btn").on("click", function() { dispatch(this, dowork, 'working', 'done!'); });
function dispatch(me, work, working, done) {
/* work function, working message HTML string, done message HTML string */
/* only designed for a <button></button> element */
var pause = 50, old;
if (!me || me.tagName.toLowerCase() != 'button' || me.innerHTML == working) return;
old = me.innerHTML;
me.innerHTML = working;
setTimeout(function() {
work();
me.innerHTML = done;
setTimeout(function() { me.innerHTML = old; }, 1500);
}, pause);
}
function dowork() {
for (var i = 1; i<1000000000; i++) {
//
}
}
Note: the dispatching function also blocks calls from happening at the same time, because it can seriously confuse users if status updates from multiple clicks are happening together.
Fake an ajax request
function longrunningfunction() {
document.getElementById("myspan").innerHTML = "doing some work";
document.getElementById("mybutt").disabled = true;
document.getElementById("mybutt").className = "buttonDisabled";
$.ajax({
url: "/",
complete: function () {
//long running task here
document.getElementById("myspan").innerHTML = "done";
}
});}
Try this
function longRunningTask(){
// Do the task here
document.getElementById("mybutt").value = "done";
}
function longrunningfunction() {
document.getElementById("mybutt").value = "doing some work";
setTimeout(function() {
longRunningTask();
}, 1);
}
Some browsers don't handle onclick html attribute good. It's better to use that event on js object. Like this:
<button id="mybutt" class="buttonEnabled">
<span id="myspan">do some work</span>
</button>
<script type="text/javascript">
window.onload = function(){
butt = document.getElementById("mybutt");
span = document.getElementById("myspan");
butt.onclick = function () {
span.innerHTML = "doing some work";
butt.disabled = true;
butt.className = "buttonDisabled";
//long running task here
span.innerHTML = "done";
};
};
</script>
I made a fiddle with working example http://jsfiddle.net/BZWbH/2/
Have you tried adding listener to "onmousedown" to change the button text and click event for longrunning function.
Slightly modified your code at jsfiddle and:
$("#btn").on("click", dowork);
function dowork() {
document.getElementById("btn").innerHTML = "working";
setTimeout(function() {
for (var i = 1; i<1000000000; i++) {
//
}
document.getElementById("btn").innerHTML = "done!";
}, 100);
}
Timeout set to more reasonable value 100ms did the trick for me. Try it.
Try adjusting the latency to find the best value.
DOM buffer also exists in default browser on android,
long running javascript only flush DOM buffer once,
use setTimeout(..., 50) to solve it.
I have adapted Estradiaz's double animation frame method for async/await:
async function waitForDisplayUpdate() {
await waitForNextAnimationFrame();
await waitForNextAnimationFrame();
}
function waitForNextAnimationFrame() {
return new Promise((resolve) => {
window.requestAnimationFrame(() => resolve());
});
}
async function main() {
const startTime = performance.now();
for (let i = 1; i <= 5; i++) {
setStatus("Step " + i);
await waitForDisplayUpdate();
wasteCpuTime(1000);
}
const elapsedTime = Math.round(performance.now() - startTime);
setStatus(`Completed in ${elapsedTime} ms`);
}
function wasteCpuTime(ms) {
const startTime = performance.now();
while (performance.now() < startTime + ms) {
if (Math.random() == 0) {
console.log("A very rare event has happened.");
}
}
}
function setStatus(s) {
document.getElementById("status").textContent = s;
}
document.addEventListener("DOMContentLoaded", main);
Status: <span id="status">Start</span>
Question sounds quiet weird I know but here is the problem, the following code works perfectly. Timer starts at 30 minutes, every second a mouse move is not detected counts the timer down. When a mouse move is detected timer gets reset to 30 minutes, at the 25 minute mark of page inactivity a CSS popup shows counting down the last 5 minutes, at 30 minutes, the user gets auto logged out. However, if the user has the page open but is actively viewing another webpage altogether the timer either slows or stops altogether depending on the browser. Which in effect negates the script altogether. Is it possible to have the script continue its normal countdown and still force the user out of the page even if they aren't actively viewing the page? Or are these browser quirks to reduce memory load?
var Timing = 0;
var CounterTime = 0;
var TimePast = 0;
var Seconds = 1800;
var Warn = 1500;
var MinuteLeft = 30;
var SecondLeft = 60;
var StopRefresh = 0;
function ResponseTime()
{
Timing = Timing + 100;
CounterTime = CounterTime + 100;
if(Timing % 1000 == 0)
{
TimePast = TimePast + 1;
SecondLeft = SecondLeft - 1;
if(SecondLeft == 59)
{
MinuteLeft = MinuteLeft-1;
}
if(SecondLeft == 0)
{
SecondLeft = 60;
}
}
if(MinuteLeft != 0)
{
if(SecondLeft == 60)
{
document.getElementById('CountdownTimer').firstChild.nodeValue = MinuteLeft+":00";
}else if(SecondLeft < 10)
{
document.getElementById('CountdownTimer').firstChild.nodeValue = MinuteLeft+":0"+SecondLeft;
}else
{
document.getElementById('CountdownTimer').firstChild.nodeValue = MinuteLeft+":"+SecondLeft;
}
if((MinuteLeft == 0) && (SecondLeft <= 10))
{
document.getElementById('CountdownTimer').style.fontWeight = "bolder";
document.getElementById('CountdownTimer').style.color = "red";
}
document.getElementById('CountdownTimer').style.fontWeight = "normal";
document.getElementById('CountdownTimer').style.color = "black";
}else
{
document.getElementById('CountdownTimer').firstChild.nodeValue = SecondLeft;
if((MinuteLeft == 0) && (SecondLeft <= 10))
{
document.getElementById('CountdownTimer').style.fontWeight = "bolder";
document.getElementById('CountdownTimer').style.color = "red";
}else
{
document.getElementById('CountdownTimer').style.fontWeight = "normal";
document.getElementById('CountdownTimer').style.color = "black";
}
}
if(TimePast == 1800)
{
document.getElementById('DoLogoutRequest').submit();
}
if(MinuteLeft <=4)
{
document.getElementById('Overlay').style.visibility="visible";
document.getElementById('ForceLogout').style.visibility="visible";
}else
{
document.getElementById('Overlay').style.visibility="hidden";
document.getElementById('ForceLogout').style.visibility="hidden";
}
$(document).ready(function(){
$(document).mousemove(function(){
Timing = 0;
TimePast = 0;
SecondLeft = 60;
MinuteLeft = 29;
});
});
}
What you could do is modify the script so that when a mousemove is detected, you first check the current number of seconds (using the Date object) since your last mousemove event.
If it's greater than 30 minutes, then you know the individual should be logged out, and then you can take that action immediately.
Think of this like setting a tripwire that is armed at the 30 second mark but doesn't fire until someone trips it.
However, with that said, I really have strong concerns about how secure this methodology is. In general, the client side code is insecure. Things like automatically logging out a user should really be handled on the server side using a session.
Still, this approach is creative in that it doesn't force me to visit a different page. So, another technique you could use that would combine the server-side approach with the mouseevent approach would be to store the mouse movements, and the time, in a variable. Then, at your 29:30 minute mark, if the array contains a mouse movement that occurred in the last 25 minutes, make a secure AJAX request to the server to tell the session that the user is still active.
This would reduce load on the server, since you're only making that update when it's needed, and it would also allow your users to use the application without needing to refresh to prevent logout, and it would also keep the actual "Is the user logged in" part of the logic where it belongs, on the server. If the server never hears a response from the client, the server will log the user out.
In summary, instead of your server waiting potentially forever to hear that it's okay to log the user out:
if(TimePast == 1800)
{
document.getElementById('DoLogoutRequest').submit();
}
The server is taking a much more authoritative approach in moving on without you, if it doesn't hear your client check-in:
if(TimePast <= 1800 && TimePast >= 1700)
{
// send keepalive request to the server to prevent auto-logout
}