How to detect idle time in JavaScript

Is it possible to detect "idle" time in JavaScript?

My primary use case probably would be to pre-fetch or preload content.

I define idle time as a period of user inactivity or without any CPU usage

Solution 1:

Here is a simple script using jQuery that handles mousemove and keypress events. If the time expires, the page reloads.

<script type="text/javascript">
    var idleTime = 0;
    $(document).ready(function () {
        // Increment the idle time counter every minute.
        var idleInterval = setInterval(timerIncrement, 60000); // 1 minute

        // Zero the idle timer on mouse movement.
        $(this).mousemove(function (e) {
            idleTime = 0;
        });
        $(this).keypress(function (e) {
            idleTime = 0;
        });
    });

    function timerIncrement() {
        idleTime = idleTime + 1;
        if (idleTime > 19) { // 20 minutes
            window.location.reload();
        }
    }
</script>

Solution 2:

Without using jQuery, only vanilla JavaScript:

var inactivityTime = function () {
    var time;
    window.onload = resetTimer;
    // DOM Events
    document.onmousemove = resetTimer;
    document.onkeydown = resetTimer;

    function logout() {
        alert("You are now logged out.")
        //location.href = 'logout.html'
    }

    function resetTimer() {
        clearTimeout(time);
        time = setTimeout(logout, 3000)
        // 1000 milliseconds = 1 second
    }
};

And initialise the function where you need it (for example: onPageLoad).

window.onload = function() {
  inactivityTime();
}

You can add more DOM events if you need to. Most used are:

document.onload = resetTimer;
document.onmousemove = resetTimer;
document.onmousedown = resetTimer; // touchscreen presses
document.ontouchstart = resetTimer;
document.onclick = resetTimer;     // touchpad clicks
document.onkeydown = resetTimer;   // onkeypress is deprectaed
document.addEventListener('scroll', resetTimer, true); // improved; see comments

Or register desired events using an array

window.addEventListener('load', resetTimer, true);
var events = ['mousedown', 'mousemove', 'keypress', 'scroll', 'touchstart'];
events.forEach(function(name) {
 document.addEventListener(name, resetTimer, true);
});

DOM Events list: http://www.w3schools.com/jsref/dom_obj_event.asp

Remember to use window, or document according your needs. Here you can see the differences between them: What is the difference between window, screen, and document in JavaScript?

Code Updated with @frank-conijn and @daxchen improve: window.onscroll will not fire if scrolling is inside a scrollable element, because scroll events don't bubble. In window.addEventListener('scroll', resetTimer, true), the third argument tells the listener to catch the event during the capture phase instead of the bubble phase.