Ben Nadel
On User Experience (UX) Design, JavaScript, ColdFusion, Node.js, Life, and Love.
Ben Nadel at cf.Objective() 2014 (Bloomington, MN) with: Shawn Grigson
Ben Nadel at cf.Objective() 2014 (Bloomington, MN) with: Shawn Grigson@shawngrig )

Trapping The Wheel Event May Prevent Chrome Browser Bug In Which The Scroll Wheel Stops Working In Overflow Container

By Ben Nadel on

A couple of weeks ago, I looked at a peculiar behavior that I was seeing in the Chrome Browser in which the scroll wheel seemed to suddenly stop working (something that I was easily able to reproduce on video). In the comments to that post, Sean Roberts theorized that the underlying issue was that Chrome was trying to apply the scroll behavior to an ancestor element because the overflow container ran out of "scollability". Piggy-backing on Sean's theory, I wanted to see if I could counter-act the bug by preventing the default "wheel" behavior if the wheel event wouldn't result in the scrolling of the overflow container. The hope being that if I tell Chrome not to apply the no-op wheel event, the browser may not get confused as to where and how to apply subsequent wheel events.


 
 
 

 
 
 
 
 

Run this demo in my JavaScript Demos project on GitHub.

View this code in my JavaScript Demos project on GitHub.

This is not the first time that I've looked at preventing the default behavior of the Wheel event in order to influence the scrolling of a page. In fact, last year, I created an Angular attribute-directive that would trap scrolling in a given container. This is particularly nice for user interfaces (UI) that have side-bars, pop-ups, and other "fly-outs" that can be scrolled. By trapping the scroll behavior in a said containers, we prevent the unexpected and jarring scroll of the Body element.

For this exploration, I want to use the same exact approach. When the user triggers a "wheel" event on the overflow container, I want to inspect the wheel event to see if has the potential to cause scrolling in the overflow container. If it can, I let the event propagate unaltered; but, if the overflow container has no more remaining offset in the relevant direction, I want to cancel the default behavior of the wheel event.

CAUTION: The very fact of having a "wheel" event listener can hurt the scroll performance (see Chrome's warning about "passive" event handlers in the developer console). As such, reacting to the "wheel" event should be done judiciously.

With that said, here's the code for my experiment. I have two overflow containers: one that has no special behavior - my "control"; and, one that traps the "wheel" event and conditionally prevents the default behavior:

  • <!doctype html>
  • <html lang="en">
  • <head>
  • <meta charset="utf-8" />
  • <title>
  • Trapping The Wheel Event May Prevent Chrome Browser Bug In Which The Scroll Wheel Stops Working In Overflow Container
  • </title>
  •  
  • <style type="text/css">
  •  
  • html {
  • box-sizing: border-box ;
  • }
  •  
  • *, *:before, *:after {
  • box-sizing: inherit ;
  • }
  •  
  • .layout {
  • background-color: #ffffff ;
  • border: 2px solid #cccccc ;
  • height: 500px ;
  • margin: -250px 0px 0px 0px ;
  • position: absolute ;
  • top: 50% ;
  • width: 300px ;
  • }
  •  
  • .layout--a {
  • right: 51% ;
  • }
  •  
  • .layout--b {
  • left: 51% ;
  • }
  •  
  • .layout__top-panel {
  • bottom: 100px ;
  • left: 0px ;
  • overflow: auto ; /* The panel becomes SCROLLABLE due to content overflow. */
  • position: absolute ;
  • right: 0px ;
  • top: 0px ;
  • }
  •  
  • .layout__bottom-panel {
  • border-top: 1px solid #cccccc ;
  • bottom: 0px ;
  • height: 100px ;
  • left: 0px ;
  • padding: 20px 20px 20px 20px ;
  • position: absolute ;
  • right: 0px ;
  • }
  •  
  • .content p {
  • margin: 0px 0px 0px 0px ;
  • padding: 25px 20px 22px 20px ;
  • }
  •  
  • .content p:nth-child( even ) {
  • background-color: #f0f0f0 ;
  • }
  •  
  • </style>
  • </head>
  • <body>
  •  
  • <h1>
  • Trapping The Wheel Event May Prevent Chrome Browser Bug In Which The Scroll Wheel Stops Working In Overflow Container
  • </h1>
  •  
  • <!-- BEGIN: Layout-A. -->
  • <section class="layout layout--a">
  • <div class="layout__top-panel">
  •  
  • <div class="content">
  • <p>Content</p><p>Content</p><p>Content</p><p>Content</p><p>Content</p>
  • <p>Content</p><p>Content</p><p>Content</p><p>Content</p><p>Content</p>
  • <p>Content</p><p>Content</p><p>Content</p><p>Content</p><p>Content</p>
  • <p>Content</p><p>Content</p><p>Content</p><p>Content</p><p>Content</p>
  • </div>
  •  
  • </div>
  • <div class="layout__bottom-panel">
  •  
  • No Behavior Modification
  •  
  • </div>
  • </section>
  • <!-- END: Layout-A. -->
  •  
  • <!-- BEGIN: Layout-B. -->
  • <section class="layout layout--b">
  • <div class="layout__top-panel">
  •  
  • <div class="content">
  • <p>Content</p><p>Content</p><p>Content</p><p>Content</p><p>Content</p>
  • <p>Content</p><p>Content</p><p>Content</p><p>Content</p><p>Content</p>
  • <p>Content</p><p>Content</p><p>Content</p><p>Content</p><p>Content</p>
  • <p>Content</p><p>Content</p><p>Content</p><p>Content</p><p>Content</p>
  • </div>
  •  
  • </div>
  • <div class="layout__bottom-panel">
  •  
  • Trapping Wheel Event
  •  
  • </div>
  • </section>
  • <!-- END: Layout-B. -->
  •  
  • <script type="text/javascript">
  •  
  • // Theoretically, the "wheel" event and the "scroll" event should go hand-in-hand
  • // as long as there is room to scroll the content of a container. However, in
  • // Chrome, the scrolling of the mouse-wheel will suddenly stop working (at least
  • // as of Chrome/70.0.3538.110). In that case, we can see the "wheel" event being
  • // logged without a corresponding "scroll" event.
  •  
  • window.addEventListener(
  • "wheel",
  • function handleWheelEvent( event ) {
  •  
  • var direction = ( event.deltaY >= 0 )
  • ? "DOWN"
  • : "UP"
  • ;
  •  
  • console.log( "Event: wheel,", direction, event.target );
  •  
  • },
  • true
  • );
  •  
  • window.addEventListener(
  • "scroll",
  • function handleScrollEvent( event ) {
  •  
  • console.log( "Event: scroll" );
  •  
  • },
  • true
  • );
  •  
  • // --------------------------------------------------------------------------- //
  • // --------------------------------------------------------------------------- //
  •  
  • // One theory as to why the scroll wheel stops working is that Chrome is getting
  • // confused as to which element it needs to apply the scroll action to. If you
  • // have nested scrollable elements then on each scroll action, the browser will
  • // try to apply the scroll to the parent element if the nested element runs out
  • // of offset. As such, let's see if we can "fix the bug" by prevent the WHEEL
  • // event's default behavior in the parent. That is, if the nested element runs
  • // out of scrollable offset, let's prevent the current WHEEL event so as to
  • // prevent Chrome from trying to apply the event to the parent container (ie, the
  • // BODY in this case).
  •  
  • // Since this bug only applies to Chrome, let's bail-out if we're not in chrome.
  • if ( isChromeBrowser() ) {
  •  
  • // This is the DOM element that is going to trap WHEEL events.
  • var panel = document.querySelector( ".layout--b .layout__top-panel" );
  •  
  • panel.addEventListener(
  • "wheel",
  • function handleWheelEvent( event ) {
  •  
  • // The wheel event represents some requested delta in a given
  • // direction. Get the direction from the event so that we can
  • // calculate whether or not to let the wheel event "happen".
  • var direction = getDirectionFromEvent( event );
  •  
  • // If the panel is already scrolled to its directional maximum, then
  • // we run the risk of Chrome trying to parle the wheel event into a
  • // scroll action on a parent container. As such, prevent the default
  • // behavior of the wheel event when we know it can't be applied to
  • // the panel.
  • if ( isScrolledInMaxDirection( panel, direction ) ) {
  •  
  • console.warn( "Preventing WHEEL event default behavior." );
  • event.preventDefault();
  •  
  • }
  •  
  • // CAUTION: Binding to the WHEEL event can have a negative impact on
  • // the smooth scrolling experience of the browser since the browser
  • // has to block and wait to see if the event is being "prevented." As
  • // such, this approach should be used judiciously.
  •  
  • },
  • false
  • );
  •  
  • } else {
  •  
  • console.warn( "Not trapping wheel - this is not the CHROME browser." );
  •  
  • }
  •  
  • // --------------------------------------------------------------------------- //
  • // --------------------------------------------------------------------------- //
  •  
  • // I get the direction, "UP" or "DOWN", from the given event.
  • function getDirectionFromEvent( event ) {
  •  
  • var delta = ( event.deltaY || event.detail );
  •  
  • return( ( delta <= 0 ) ? "UP" : "DOWN" );
  •  
  • }
  •  
  •  
  • // I determine if the given element is scrolled to the maximum offset in the
  • // given direction ("UP" or "DOWN").
  • function isScrolledInMaxDirection( element, direction ) {
  •  
  • if ( direction === "UP" ) {
  •  
  • return( ! element.scrollTop );
  •  
  • } else {
  •  
  • return( ( element.clientHeight + element.scrollTop ) >= element.scrollHeight );
  •  
  • }
  •  
  • }
  •  
  •  
  • // I use feature detection to determine if the current browser is Chrome.
  • function isChromeBrowser() {
  •  
  • return( !! ( window.chrome && window.chrome.webstore ) );
  •  
  • }
  •  
  • </script>
  •  
  • </body>
  • </html>

As you can see, for each wheel event in the layout-b, I'm looking to see which direction the wheel is moving. Then, I check to see if the "scrollTop" of the overflow container can be adjusted in said direction. If not, I prevent the default behavior of the "wheel" event; which, in turn, will prevent the "scroll" event from happening.

This manipulated behavior can be seen in the console logging:


 
 
 

 
 Preventing the default behavior of the wheel event helps counter-act a bug in Chrome in which the scrolling of an overflow container stops working. 
 
 
 

Now, it's really hard to actually prove that this approach makes a difference. But, I can consistently reproduce the scrolling problem in the "control" layout; and, I have yet to reproduce the scrolling problem in the layout that traps and consumes the wheel event. As such, I feel comfortable saying that this approach has a positive influence on the Chrome scrolling bug (even if I can't say that this approach fixes the problem entirely).

Of course, it's a trade-off: does the potential jank of a wheel-interception workflow outweigh the potential jank of the scroll effect not being applied to the expected element? Each use-case will be different.

Wouldn't it be awesome if HTML just had some sort of element property that told the browser to trap scrolling? I can't be the only one who feels this way.



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