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Replace dropdown backdrop hack with cleaner JS-only hack

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* Replace backdrop with simple noop mouse listener

As discussed in https://github.com/twbs/bootstrap/pull/22422 the current
approach of injecting a backdrop (to work around iOS' broken event
delegation for the `click` event) has annoying consequences on
touch-enabled laptop/desktop devices.
Instead of a backdrop `<div>`, here we simply add extra empty/noop
mouse listeners to the immediate children of `<body>` (and remove
them when the dropdown is closed) in order to force iOS to properly
bubble a `click` resulting from a tap (essentially, method 2 from
https://www.quirksmode.org/blog/archives/2014/02/mouse_event_bub.html)
This is sufficient (except in rare cases where the user does manage to tap
on the body itself, rather than any child elements of body - which is not
very likely in an iOS phone/tablet scenario for most layouts) to get iOS to
get a grip and do the correct event bubbling/delegation, meaning the regular
"click" event will bubble back to the `<body>` when tapping outside of the dropdown,
and the dropdown will close properly (just like it already does, even without
this fix, in non-iOS touchscreen devices/browsers, like Chrome/Android and
Windows on a touch laptop).
This approach, though a bit hacky, has no impact on the DOM structure, and
has no unforeseen side effects on touch-enabled laptops/desktops. And crucially,
it works just fine in iOS.

* Remove dropdown backdrop styles

* Update doc for dropdowns and touch-enabled devices
This commit is contained in:
Patrick H. Lauke
2017-04-14 09:19:00 +01:00
committed by GitHub
parent 3b3366e1b6
commit 6d64afe508
4 changed files with 12 additions and 26 deletions
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docs/components/dropdowns.md
+3 -1
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@@ -480,7 +480,9 @@ Add `.disabled` to items in the dropdown to **style them as disabled**.
Via data attributes or JavaScript, the dropdown plugin toggles hidden content (dropdown menus) by toggling the `.show` class on the parent list item.
On touch-enabled devices, opening a dropdown adds a `.dropdown-backdrop` as a tap area for closing dropdown menus when tapping outside the menu, to work around a quirk in iOS' event delegation. **This means that once a dropdown menu is open, any tap or click (including with a mouse, on a multi-input device such as a laptop with a touchscreen) outside of the menu will be intercepted to close the menu. Opening another dropdown menu, or activating any other control or link, will therefore require an extra tap or click.**
{% callout info %}
On touch-enabled devices, opening a dropdown adds empty (`$.noop`) `mouseover` handlers to the immediate children of the `<body>` element. This admittedly ugly hack is necessary to work around a [quirk in iOS' event delegation](https://www.quirksmode.org/blog/archives/2014/02/mouse_event_bub.html), which would otherwise prevent a tap anywhere outside of the dropdown from triggering the code that closes the dropdown. Once the dropdown is closed, these additional empty `mouseover` handlers are removed.
{% endcallout %}
Note: The `data-toggle="dropdown"` attribute is relied on for closing dropdown menus at an application level, so it's a good idea to always use it.