1253484 - Mouse wheel incorrectly scrolls all sections with narrow scrollbar on http://vk.com/

Status: NEW

(Core :: DOM: Events, defect, P3)

Description

[arni2033]

>>>   My Info:   Win7_64, Nightly 47, 32bit, ID 20160229030448
STR:

>>  If you don't want to log in, skip Steps 0,2,3. vk.com is social network, ~75million daily users
0. (optional) log in on http://vk.com/
1. Set mouse option "when I rotate mouse wheel" in your OS to "scroll by 1 page"

2. Test emoji section
 2.1. Open https://vk.com/im?sel=<your_id> with your ID instead of <your_id>
 2.2. Hover mouse over the smiley next in the entry field, wait until emoji section appears
 2.3. Drag the scrollbar in that section to the very end. Drag scrollbar to the beginning.
 2.4. Hover mouse over emoji section. Rotate mouse wheel down once. Rotate mouse wheel up once.

3. Test music section
 3.1. Click "Music" button at the top side of the page
 3.2. Click "Popular" in the right sidebar
 3.3. Drag the scrollbar to the very end of music section
 3.4. If there's button "Show more", then click it and go to Step 3.3. Otherwise go to Step 3.5.
 3.5. Drag the scrollbar to the beginning
 3.6. Hover mouse over music section. Rotate mouse wheel down once. Rotate mouse wheel up once.

4. Test "Recent news" section
 4.1. Open https://vk.com/ads
 4.2. In the "Recent news" block at the right
 4.3. Hover mouse over scrollbar, hold left mouse button, move mouse to the bottom of the screen,
      keep moving mouse to the left and to the right for 5 seconds to scroll the
      "Recent news" block to the end
 4.4. Move mouse to the top side of the screen to drag the scrollbar to the beginning.
 4.5. Release left mouse button
 4.6. Hover mouse over recent news. Rotate mouse wheel down once. Rotate mouse wheel up once.

5. Test playlist section
 5.1. Open https://vk.com/webmproject
 5.2. Click on video title (below any video) to open it in "maximized mode"
 5.3. Stop the video immediately: there may be some really stupid videos.
 5.4. Drag the thin scrollbar at the right side of playlist section to the very end
 5.5. Drag the scrollbar to the beginning
 5.6. Hover mouse over playlist section. Rotate mouse wheel down once. Rotate mouse wheel up once


AR:  2,3,4,5:  section is scrolled to the very end, then to the very beginning
ER:  Section should be scrolled a bit to the bottom. Just a bit, by ~1 item

Notes:
1) This also happens with all sections with narrow scrollbar, e.g. minified messages history
2) Request screencast(s) if necessary.
3) Firefox works OK if I set the mouse option (Step 1) to "Scroll by 3 lines"
   It still breaks if I set the mouse option to "Scroll by 46 lines"
4) IE11 and GoogleChrome work fine with any value of the mouse option (Step 1)  [OK]

Comment 3

[Andrew Overholt [:overholt]]

smaug, wdyt?

Comment 4

[Olli Pettay [:smaug][[e-mail]]]

So isn't this a dup of the other bug you arni filed about 'in your OS to "scroll by 1 page"'
where pages are using legacy DOMMouseScroll event which is Gecko only and they aren't using it per its API. 
We may or may not want to change the behavior.

Reporter, could you perhaps help here a bit and check which events the website is using.
I assume it is using DOMMouseScroll.

One thing we should probably do is to add telemetry about how many users have OS' scroll setting something uncommon, like that "scroll by 1 page"

Comment 5

[arni2033]

This is DOMMouseScroll, yes. I tested and filed all issues related to DOMMouseScroll in product "Core", not "tech evangelism", to show that it's really hard for web developers to understand some special cases in API which they can't test on their own machine.
The related line of code:   http://vk.com/js/api/widgets/al_community.js , lines 637 and 638
>              637   w.Scrollbar.prototype.wheel = function(event) {
> [breakpoint] 638     if (!event) event = window.event;

Comment 6

[Andrew Overholt [:overholt]]

(In reply to Olli Pettay [:smaug] from comment #4)
> One thing we should probably do is to add telemetry about how many users
> have OS' scroll setting something uncommon, like that "scroll by 1 page"

^ idea for something someone can do.

Comment 7

[arni2033]

(In reply to Olli Pettay [:smaug] from comment #4)
> One thing we should probably do is to add telemetry about how many users have OS' scroll setting
> something uncommon, like that "scroll by 1 page"
And then what? If there's a small amount of people, you will leave things "as is"???
Then WHY did you set this trap for such a small amount of people?!!! INCLUDING ME! Jesus Christ...

Though you may want to know about bug 1238502 comment 10