How to detect idle time in JavaScript elegantly?

Question

Is it possible to detect \"idle\" time in JavaScript?
My primary use case probably would be to pre-fetch or preload content.

Idle time:

Answer 1

Without using jQuery, only vanilla JavaScript:

var inactivityTime = function () {
    var time;
    window.onload = resetTimer;
    // DOM Events
    document.onmousemove = resetTimer;
    document.onkeypress = 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 init 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 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. window.addEventListener('scroll', resetTimer, true), the third argument tells the listener to catch event during capture phase instead of bubble phase.