Detect whether scroll event was created by user

Rather than trying to catch all the user events, it's much easier to do the opposite and handle only the programmatic events - and ignore those.

For example, this kind of code would work:

// Element that needs to be scrolled
var myElement = document.getElementById('my-container');

// Flag to tell if the change was programmatic or by the user
var ignoreNextScrollEvent = false;

function setScrollTop(scrollTop) {
    ignoreNextScrollEvent = true;
    myElement.scrollTop = scrollTop
}

myElement.addEventListener('scroll', function() {
    if (ignoreNextScrollEvent) {
        // Ignore this event because it was done programmatically
        ignoreNextScrollEvent = false;
        return;
    }

    // Process user-initiated event here
});

Then when you call setScrollTop(), the scroll event will be ignored, while if the user scroll with the mouse, keyboard or any other way, the event will be processed.


Unfortunately, there is no direct way of telling that.

I would say if you can redesign your app so that it doesn't depend on this type of flow, go for that.

If not, a workaround I can think of is to keep track of user initiated scrolls and check that to see if the scroll was triggered by the browser or by the user.

Here's an example that I put together which does this pretty well (except for browsers where jQuery history has problems with).

You need to run this locally to be able to test it fully (jsFiddle/jsbin are not good fits as they iFrame the contents).

Here's the test cases that I validated:

  • Page loads - userScroll is false
  • Scroll using mouse/keyboard - userScroll becomes true
  • Click on the link to jump to page bottom - userScroll becomes false
  • Click Back/Forward - userScroll becomes false;
<!DOCTYPE html> 
<html lang="en"> 
<head> 
    <meta charset="utf-8" /> 
    <script src="http://code.jquery.com/jquery-1.6.1.min.js"></script> 
    <script type="text/javascript" src="https://raw.github.com/tkyk/jquery-history-plugin/master/jquery.history.js"></script> 
</head> 
<body> 
    <span> hello there </span><br/> 
    <a href="#bottom"> click here to go down </a> 
    <br/><br/><br/><br/><br/><br/><br/><br/><br/><br/><br/><br/><br/><br/><br/> 
    <br/><br/><br/><br/><br/><br/><br/><br/><br/><br/><br/><br/><br/><br/><br/> 
    <br/><br/><br/><br/><br/><br/><br/><br/><br/><br/><br/><br/><br/><br/><br/> 
    <br/><br/><br/><br/><br/><br/><br/><br/><br/><br/><br/><br/><br/><br/><br/> 
    <br/><br/><br/><br/><br/><br/><br/><br/><br/><br/><br/><br/><br/><br/><br/> 
    <br/><br/><br/><br/><br/><br/><br/><br/><br/><br/><br/><br/><br/><br/><br/> 
    <br/><br/><br/><br/><br/><br/><br/><br/><br/><br/><br/><br/><br/><br/><br/> 
    <a name="bottom"> just sitting </a> 
</body> 
<script type="text/javascript"> 

var userScroll = false;     

function mouseEvent(e) { 
    userScroll = true; 
} 


$(function() { 

    // reset flag on back/forward 
    $.history.init(function(hash){ 
        userScroll = false; 
    }); 

    $(document).keydown(function(e) { 
        if(e.which == 33        // page up 
           || e.which == 34     // page dn 
           || e.which == 32     // spacebar
           || e.which == 38     // up 
           || e.which == 40     // down 
           || (e.ctrlKey && e.which == 36)     // ctrl + home 
           || (e.ctrlKey && e.which == 35)     // ctrl + end 
          ) { 
            userScroll = true; 
        } 
    }); 

    // detect user scroll through mouse
    // Mozilla/Webkit 
    if(window.addEventListener) {
        document.addEventListener('DOMMouseScroll', mouseEvent, false); 
    }

    //for IE/OPERA etc 
    document.onmousewheel = mouseEvent; 


    // to reset flag when named anchors are clicked
    $('a[href*=#]').click(function() { 
        userScroll = false;
    }); 

      // detect browser/user scroll
    $(document).scroll( function(){  
        console.log('Scroll initiated by ' + (userScroll == true ? "user" : "browser"));
    });
}); 
</script> 
</html>

Notes:

  • This doesn't track scrolling when the user drags the scrollbar with mouse. This can be added with some more code, which I left as an exercise for you.
  • event.keyCodes may vary by OS, so you may have to change that appropriately.

Hope this helps!


As far as I know it is impossible (without any work) to tell whenever scroll event has been issued by "user" or by other means.

You could try (as others mentioned) catch mousewheel events, then probably trying to catch keydown event on any keys that can trigger scroll (arrows, space etc.) while checking what element is currently focused, since you for example can't scroll using arrow keys while typing in an input field. In general that would be complex and messy script.

Depending on situation you're dealing with you could I guess "revert the logic", and instead of detecting user issued scroll events just hook in into any scrolls made programatically and treat any scroll events not made by your code as made by an user. Like I said it depends on a situation, and what you're trying to achive.

Tags:

Javascript

Jquery

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