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Remove `touch-action:manipulation` click optimization (#25250)

Due to a severe performance bug in Chrome (see https://bugs.chromium.org/p/chromium/issues/detail?id=800522) and due to the fact that (with the exception of IE/Edge on Windows desktop with touchscreen) all modern browsers now optimize the click delay away anyway, this optimization is not needed.

Closes #24670
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patrickhlauke committed Jan 11, 2018
1 parent bfceedc commit 2e15b9488874d8c129e6bd4da0425ecbac359c03
Showing with 1 addition and 38 deletions.
  1. +1 −15 docs/4.0/content/reboot.md
  2. +0 −23 scss/_reboot.scss
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@@ -363,18 +363,4 @@ HTML5 adds [a new global attribute named `[hidden]`](https://developer.mozilla.o
`[hidden]` is not compatible with jQuery's `$(...).hide()` and `$(...).show()` methods. Therefore, we don't currently especially endorse `[hidden]` over other techniques for managing the `display` of elements.
{% endcallout %}
To merely toggle the visibility of an element, meaning its `display` is not modified and the element can still affect the flow of the document, use [the `.invisible` class]({{ site.baseurl }}/docs/{{ site.docs_version }}/utilities/visibility/) instead.
## Click delay optimization for touch
Traditionally, browsers on touchscreen devices have a delay of approximately 300ms between the end of a "tap" – the moment when a finger/stylus is lifted from screen – and the [`click` event](https://developer.mozilla.org/en-US/docs/Web/Events/click) being fired. This delay is necessary for these browsers to correctly handle "double-tap to zoom" gestures without prematurely triggering actions or links after the first "tap", but it can make your site feel slightly sluggish and unresponsive.
Most mobile browsers automatically optimize away this 300ms delay for sites that use the `width=device-width` property as part of their [responsive meta tag]({{ site.baseurl }}/docs/{{ site.docs_version }}/getting-started/introduction/#responsive-meta-tag) (as well as for sites that disable zooming, for instance with `user-scalable=no`, though this practice is strongly discouraged for accessibility and usability reasons). The biggest exceptions here are IE11 on Windows Phone 8.1, and iOS Safari (and any other iOS WebView-based browser) [prior to iOS 9.3](https://webkit.org/blog/5610/more-responsive-tapping-on-ios/).
On touch-enabled laptop/desktop devices, IE11 and Microsoft Edge are currently the only browsers with "double-tap to zoom" functionality. As the [responsive meta tag]({{ site.baseurl }}/docs/{{ site.docs_version }}/getting-started/introduction/#responsive-meta-tag) is ignored by all desktop browsers, using `width=device-width` will have no effect on the 300ms delay here.
To address this problem in IE11 and Microsoft Edge on desktop, as well as IE11 on Windows Phone 8.1, Bootstrap explicitly uses the [`touch-action:manipulation` CSS property](https://developer.mozilla.org/en-US/docs/Web/CSS/touch-action) on all interactive elements (such as buttons and links). This property essentially disables double-tap functionality on those elements, eliminating the 300ms delay.
In the case of old iOS versions (prior to 9.3), the suggested approach is to use additional scripts such as [FastClick](https://github.com/ftlabs/fastclick) to explicitly work around the delay.
For further details, see the compatibility table for [suppressing 300ms delay for touchscreen interactions](https://patrickhlauke.github.io/touch/tests/results/#suppressing-300ms-delay).
To merely toggle the visibility of an element, meaning its `display` is not modified and the element can still affect the flow of the document, use [the `.invisible` class]({{ site.baseurl }}/docs/{{ site.docs_version }}/utilities/visibility/) instead.
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@@ -279,29 +279,6 @@ svg:not(:root) {
}
// Avoid 300ms click delay on touch devices that support the `touch-action` CSS property.
//
// In particular, unlike most other browsers, IE11+Edge on Windows 10 on touch devices and IE Mobile 10-11
// DON'T remove the click delay when `<meta name="viewport" content="width=device-width">` is present.
// However, they DO support removing the click delay via `touch-action: manipulation`.
// See:
// * https://getbootstrap.com/docs/4.0/content/reboot/#click-delay-optimization-for-touch
// * https://caniuse.com/#feat=css-touch-action
// * https://patrickhlauke.github.io/touch/tests/results/#suppressing-300ms-delay
a,
area,
button,
[role="button"],
input:not([type="range"]),
label,
select,
summary,
textarea {
touch-action: manipulation;
}
//
// Tables
//

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