How can I differentiate a manual scroll (via mousewheel/scrollbar) from a Javascript/jQuery scroll?

Question

UPDATE:

Here is a jsbin example demonstrating the problem.

UPDATE 2:
And here is the fixed version thanks to fudgey.

---

Basically, I have the following javascript which scrolls the window to an anchor on the page:

 // get anchors with href's that start with "#"
 $("a[href^=#]").live("click", function(){
     var target = $($(this).attr("href"));
     // if the target exists: scroll to it...
     if(target[0]){
         // If the page isn't long enough to scroll to the target's position
         // we want to scroll as much as we can. This part prevents a sudden 
         // stop when window.scrollTop reaches its maximum.
         var y = Math.min(target.offset().top, $(document).height() - $(window).height());
         // also, don't try to scroll to a negative value...
         y=Math.max(y,0);
         // OK, you can scroll now...
         $("html,body").stop().animate({ "scrollTop": y }, 1000);
     }
     return false;
 });

It works perfectly......until I manually try to scroll the window. When the scrollbar or mousewheel is scrolled I need to stop the current scroll animation...but I'm not sure how to do this.

This is probably my starting point...

$(window).scroll(e){
    if(IsManuallyScrolled(e)){
        $("html,body").stop();
    }
} 

...but I'm not sure how to code the IsManuallyScrolled function. I've checked out e (the event object) in Google Chrome's console and AFAIK there is not way to differentiate between a manual scroll and jQuery's animate() scroll.

How can I differentiate between a manual scroll and one called via jQuery's $.fn.animate function?

Answer 1

Try this function:

$('body,html').bind('scroll mousedown wheel DOMMouseScroll mousewheel keyup', function(e){
 if ( e.which > 0 || e.type == "mousedown" || e.type == "mousewheel"){
  $("html,body").stop();
 }
})

Also, did you see this tutorial?

Update: Modern browsers now use "wheel" as the event, so I've included it in the code above.

Answer 2

I had your same issue some a few days ago.You shouldn't be using jquery's animate function if you want to obtain that result, you have to simulate the animation using a polling function.

I made this class which is supposed to provide a smooth scrolldown when ScrollDown.slow() is called.

ScrollDown.current=$(window).scrollTop();
ScrollDown.lastValue;
ScrollDown.lastType;
ScrollDown.enabled=true;
ScrollDown.custom=function(value,rate){  //let's say value==='bottom' and rate=10
    if(value==='bottom'){
        value=$(document).height()-$(window).height();
    }
    ScrollDown.current=$(window).scrollTop();
    ScrollDown.lastValue=value;
    (function poll(){
        setTimeout(function(){
            var prev=$(window).scrollTop();  //This is the critical part
            /*I'm saving again the scroll position of the window, remember
            10 ms have passed since the polling has started
            At this rate, if the user will scroll up for down pre!==ScrollDown.current
            And that means I have to stop scrolling.*/
            ScrollDown.current++; //increasing the scroll variable so that it keeps scrolling
            $(window).scrollTop(ScrollDown.current);
            if(ScrollDown.current<ScrollDown.lastValue && ScrollDown.enabled){  
            //ScrollDown.current<ScrollDown.lastValue basically checks if it's reached the bottom
                if(prev!==ScrollDown.current-1){
                /*I'm checking if the user 
                scrolled up or down while the polling has been going on, 
                if the user scrolls up then prev<ScrollDown.current-1, 
                if the user scrolls down then prev>ScrollDown.current-1 
                and at the next poll() the scrolling will stop 
                because ScrollDown.enabled will bet set to false by ScrollDown.stop()*/
                    ScrollDown.stop();
                }
                poll();
            }
        },rate);
    })();
};

ScrollDown.stop=function(){
    ScrollDown.enabled=false;
};

ScrollDown.continue=function(){
    ScrollDown.enabled=true;
    switch (ScrollDown.lastType){
        case "fast":
            ScrollDown.fast(ScrollDown.lastValue);
            break;
        case "normal":
            ScrollDown.normal(ScrollDown.lastValue);
            break;
        case "slow":
            ScrollDown.slow(ScrollDown.lastValue);
            break;
    }
};

ScrollDown.fast=function(value){
    if(!ScrollDown.enabled){
        ScrollDown.continue();
    }else{
        ScrollDown.lastType='fast';
        ScrollDown.custom(value,1);
    }
};
ScrollDown.normal=function(value){
    if(!ScrollDown.enabled){
        ScrollDown.continue();
    }else{
        ScrollDown.lastType='normal';
        ScrollDown.custom(value,10);
    }
};
ScrollDown.slow=function(value){
    if(!ScrollDown.enabled){
        ScrollDown.continue();
    }else{
        ScrollDown.lastType='slow';
        ScrollDown.custom(value,50);
    }
};
function ScrollDown(){}

So if you were to call ScrollDown.slow('bottom') it would start scrolling slowly till it reaches the bottom of your page unless you scroll up or down manually, then it stops.

Answer 3

You could set a variable to indicate that your call to animate was active, then check that variable inside the scroll handler.

window.IsAutoScrolling = true;
$("html,body").stop().animate({ "scrollTop": y }, 1000);
// Do something to set IsAutoScrolling = false, when the animation is done.

$(window).scroll(e){  
if(!window.IsAutoScrolling){  
    $("html,body").stop();  
}