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<title>[46825] branches/5.3/src/wp-content/themes/twentytwenty: Twenty Twenty: Replace Smooth Scroll JS implementation with `scroll-behavior` CSS property.</title>
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<dl class="meta" style="font-size: 105%">
<dt style="float: left; width: 6em; font-weight: bold">Revision</dt> <dd><a style="font-weight: bold" href="https://core.trac.wordpress.org/changeset/46825">46825</a><script type="application/ld+json">{"@context":"http://schema.org","@type":"EmailMessage","description":"Review this Commit","action":{"@type":"ViewAction","url":"https://core.trac.wordpress.org/changeset/46825","name":"Review Commit"}}</script></dd>
<dt style="float: left; width: 6em; font-weight: bold">Author</dt> <dd>SergeyBiryukov</dd>
<dt style="float: left; width: 6em; font-weight: bold">Date</dt> <dd>2019-12-07 11:06:06 +0000 (Sat, 07 Dec 2019)</dd>
</dl>

<pre style='padding-left: 1em; margin: 2em 0; border-left: 2px solid #ccc; line-height: 1.25; font-size: 105%; font-family: sans-serif'>Twenty Twenty: Replace Smooth Scroll JS implementation with `scroll-behavior` CSS property.

The JS implementation had multiple issues and did not work as expected.

This change includes an accessibility enhancement by using `prefers-reduced-motion: reduce` media query property for users that don't want motion effects. For further explanation on this media query, see MDN documentation: https://developer.mozilla.org/en-US/docs/Web/CSS/scroll-behavior#Accessibility_concerns

Props audrasjb, melchoyce, joostdevalk, Anlino, mauteri, sergiomdgomes, littlebigthing, williampatton, netweb, andraganescu, joyously, acosmin, mukesh27, hareesh-pillai.
Merges <a href="https://core.trac.wordpress.org/changeset/46824">[46824]</a> to the 5.3 branch.
Fixes <a href="https://core.trac.wordpress.org/ticket/48763">#48763</a>, <a href="https://core.trac.wordpress.org/ticket/48551">#48551</a>, <a href="https://core.trac.wordpress.org/ticket/48866">#48866</a>.</pre>

<h3>Modified Paths</h3>
<ul>
<li><a href="#branches53srcwpcontentthemestwentytwentyassetsjsindexjs">branches/5.3/src/wp-content/themes/twentytwenty/assets/js/index.js</a></li>
<li><a href="#branches53srcwpcontentthemestwentytwentystylertlcss">branches/5.3/src/wp-content/themes/twentytwenty/style-rtl.css</a></li>
<li><a href="#branches53srcwpcontentthemestwentytwentystylecss">branches/5.3/src/wp-content/themes/twentytwenty/style.css</a></li>
</ul>

<h3>Property Changed</h3>
<ul>
<li><a href="#branches53">branches/5.3/</a></li>
</ul>

</div>
<div id="patch">
<h3>Diff</h3>
<span class="cx" style="display: block; padding: 0 10px">Index: branches/5.3
</span><span class="cx" style="display: block; padding: 0 10px">===================================================================
</span><del style="background-color: #fdd; text-decoration:none; display:block; padding: 0 10px">--- branches/5.3 2019-12-07 11:03:09 UTC (rev 46824)
</del><ins style="background-color: #dfd; text-decoration:none; display:block; padding: 0 10px">+++ branches/5.3  2019-12-07 11:06:06 UTC (rev 46825)
</ins><a id="branches53"></a>
<div class="propset"><h4 style="background-color: #eee; color: inherit; margin: 1em 0; padding: 1.3em; font-size: 115%">Property changes: branches/5.3</h4>
<pre class="diff"><span>
</span></pre></div>
<a id="svnmergeinfo"></a>
<div class="modfile"><h4 style="background-color: #eee; color: inherit; margin: 1em 0; padding: 1.3em; font-size: 115%">Modified: svn:mergeinfo</h4></div>
<span class="cx" style="display: block; padding: 0 10px"> /branches/3.4:21757
</span><span class="cx" style="display: block; padding: 0 10px"> /branches/4.9:43557,43622
</span><span class="cx" style="display: block; padding: 0 10px"> /branches/5.0:43681-43682,43684-43688,43719-43720,43723,43726-43727,43729-43731,43734-43744,43747,43751-43754,43758,43760-43765,43767-43770,43772,43774-43781,43783,43785,43790-43806,43808-43821,43825,43828,43830-43834,43836-43843,43846-43863,43867-43889,43891-43894,43897-43905,43908-43909,43911-43929,43931-43942,43946-43947,43949-43956,43959-43964,43967-43969,43988,43994,44014,44017,44047,44183,44185,44187-44206,44208-44213,44231-44232,44235,44248,44284,44287-44288
</span><del style="background-color: #fdd; text-decoration:none; display:block; padding: 0 10px">-/trunk:46583,46605-46606,46613,46616,46656,46658,46665,46668,46676-46677,46700-46703,46705,46707,46709,46711,46713,46715,46719-46720,46722,46724,46738,46745-46748,46753,46756-46758,46761-46762,46765,46770,46772,46779,46782,46786,46788,46793,46795,46797,46815,46817
</del><span class="cx" style="display: block; padding: 0 10px">\ No newline at end of property
</span><ins style="background-color: #dfd; text-decoration:none; display:block; padding: 0 10px">+/trunk:46583,46605-46606,46613,46616,46656,46658,46665,46668,46676-46677,46700-46703,46705,46707,46709,46711,46713,46715,46719-46720,46722,46724,46738,46745-46748,46753,46756-46758,46761-46762,46765,46770,46772,46779,46782,46786,46788,46793,46795,46797,46815,46817,46824
</ins><span class="cx" style="display: block; padding: 0 10px">\ No newline at end of property
</span><a id="branches53srcwpcontentthemestwentytwentyassetsjsindexjs"></a>
<div class="modfile"><h4 style="background-color: #eee; color: inherit; margin: 1em 0; padding: 1.3em; font-size: 115%">Modified: branches/5.3/src/wp-content/themes/twentytwenty/assets/js/index.js</h4>
<pre class="diff"><span>
<span class="info" style="display: block; padding: 0 10px; color: #888">--- branches/5.3/src/wp-content/themes/twentytwenty/assets/js/index.js        2019-12-07 11:03:09 UTC (rev 46824)
+++ branches/5.3/src/wp-content/themes/twentytwenty/assets/js/index.js  2019-12-07 11:06:06 UTC (rev 46825)
</span><span class="lines" style="display: block; padding: 0 10px; color: #888">@@ -323,98 +323,6 @@
</span><span class="cx" style="display: block; padding: 0 10px"> }; // twentytwenty.instrinsicRatioVideos
</span><span class="cx" style="display: block; padding: 0 10px"> 
</span><span class="cx" style="display: block; padding: 0 10px"> /*     -----------------------------------------------------------------------------------------------
</span><del style="background-color: #fdd; text-decoration:none; display:block; padding: 0 10px">-        Smooth Scroll
---------------------------------------------------------------------------------------------------- */
-
-twentytwenty.smoothScroll = {
-
-       init: function() {
-               // Scroll to anchor
-               this.scrollToAnchor();
-
-               // Scroll to element
-               this.scrollToElement();
-       },
-
-       // Scroll to anchor
-       scrollToAnchor: function() {
-               var anchorElements = document.querySelectorAll( 'a[href*="#"]' );
-               var anchorElementsList = Array.prototype.slice.call( anchorElements );
-               anchorElementsList.filter( function( element ) {
-                       if ( element.href === '#' || element.href === '#0' || element.id === 'cancel-comment-reply-link' || element.classList.contains( 'do-not-scroll' ) || element.classList.contains( 'skip-link' ) ) {
-                               return false;
-                       }
-                       return true;
-               } ).forEach( function( element ) {
-                       element.addEventListener( 'click', function( event ) {
-                               var target, scrollOffset, originalOffset, adminBar, scrollSpeed, additionalOffset;
-
-                               // On-page links
-                               if ( window.location.hostname === event.target.hostname ) {
-                                       // Figure out element to scroll to
-                                       target = window.location.hash !== '' && document.querySelector( window.location.hash );
-                                       target = target ? target : event.target.hash !== '' && document.querySelector( event.target.hash );
-
-                                       // Does a scroll target exist?
-                                       if ( target ) {
-                                               // Only prevent default if animation is actually gonna happen
-                                               event.preventDefault();
-
-                                               // Get options
-                                               additionalOffset = event.target.dataset.additionalOffset;
-                                               scrollSpeed = event.target.dataset.scrollSpeed ? event.target.dataset.scrollSpeed : 500;
-
-                                               // Determine offset
-
-                                               adminBar = document.querySelector( '#wpadminbar' );
-
-                                               originalOffset = target.getBoundingClientRect().top + window.pageYOffset;
-                                               scrollOffset = additionalOffset ? originalOffset + additionalOffset : originalOffset;
-
-                                               if ( adminBar && event.target.className === 'to-the-top' ) {
-                                                       scrollOffset = scrollOffset - adminBar.getBoundingClientRect().height;
-                                               }
-
-                                               twentytwentyScrollTo( scrollOffset, null, scrollSpeed );
-
-                                               window.location.hash = event.target.hash.slice( 1 );
-                                       }
-                               }
-                       } );
-               } );
-       },
-
-       // Scroll to element
-       scrollToElement: function() {
-               var scrollToElement = document.querySelector( '*[data-scroll-to]' );
-
-               if ( scrollToElement ) {
-                       scrollToElement.addEventListener( 'click', function( event ) {
-                               var originalOffset, additionalOffset, scrollOffset, scrollSpeed,
-                                       // Figure out element to scroll to
-                                       target = event.target.dataset.twentytwentyScrollTo;
-
-                               // Make sure said element exists
-                               if ( target ) {
-                                       event.preventDefault();
-
-                                       // Get options
-                                       additionalOffset = event.target.dataset.additionalOffset;
-                                       scrollSpeed = event.target.dataset.scrollSpeed ? event.target.dataset.scrollSpeed : 500;
-
-                                       // Determine offset
-                                       originalOffset = target.getBoundingClientRect().top + window.pageYOffset;
-                                       scrollOffset = additionalOffset ? originalOffset + additionalOffset : originalOffset;
-
-                                       twentytwentyScrollTo( scrollOffset, null, scrollSpeed );
-                               }
-                       } );
-               }
-       }
-
-}; // twentytwenty.smoothScroll
-
-/*     -----------------------------------------------------------------------------------------------
</del><span class="cx" style="display: block; padding: 0 10px">         Modal Menu
</span><span class="cx" style="display: block; padding: 0 10px"> --------------------------------------------------------------------------------------------------- */
</span><span class="cx" style="display: block; padding: 0 10px"> twentytwenty.modalMenu = {
</span><span class="lines" style="display: block; padding: 0 10px; color: #888">@@ -745,7 +653,6 @@
</span><span class="cx" style="display: block; padding: 0 10px">        twentytwenty.toggles.init();    // Handle toggles
</span><span class="cx" style="display: block; padding: 0 10px">        twentytwenty.coverModals.init();        // Handle cover modals
</span><span class="cx" style="display: block; padding: 0 10px">        twentytwenty.intrinsicRatioVideos.init();       // Retain aspect ratio of videos on window resize
</span><del style="background-color: #fdd; text-decoration:none; display:block; padding: 0 10px">-        twentytwenty.smoothScroll.init();       // Smooth scroll to anchor link or a specific element
</del><span class="cx" style="display: block; padding: 0 10px">         twentytwenty.modalMenu.init();  // Modal Menu
</span><span class="cx" style="display: block; padding: 0 10px">        twentytwenty.primaryMenu.init();        // Primary Menu
</span><span class="cx" style="display: block; padding: 0 10px">        twentytwenty.touchEnabled.init();       // Add class to body if device is touch-enabled
</span><span class="lines" style="display: block; padding: 0 10px; color: #888">@@ -891,49 +798,3 @@
</span><span class="cx" style="display: block; padding: 0 10px"> 
</span><span class="cx" style="display: block; padding: 0 10px">        return parents;
</span><span class="cx" style="display: block; padding: 0 10px"> }
</span><del style="background-color: #fdd; text-decoration:none; display:block; padding: 0 10px">-
-// twentytwentyEaseInOutQuad functions http://goo.gl/5HLl8
-function twentytwentyEaseInOutQuad( t, b, c, d ) {
-       t /= d / 2;
-       if ( t < 1 ) {
-               return ( ( ( c / 2 ) * t ) * t ) + b;
-       }
-       t--;
-       return ( ( -c / 2 ) * ( ( t * ( t - 2 ) ) - 1 ) ) + b;
-}
-
-function twentytwentyScrollTo( to, callback, duration ) {
-       var start, change, increment, currentTime;
-
-       function move( amount ) {
-               document.documentElement.scrollTop = amount;
-               document.body.parentNode.scrollTop = amount;
-               document.body.scrollTop = amount;
-       }
-
-       start = document.documentElement.scrollTop || document.body.parentNode.scrollTop || document.body.scrollTop;
-       change = to - start;
-       increment = 20;
-       currentTime = 0;
-
-       duration = ( typeof ( duration ) === 'undefined' ) ? 500 : duration;
-
-       function animateScroll() {
-               var val;
-
-               // increment the time
-               currentTime += increment;
-               // find the value with the quadratic in-out twentytwentyEaseInOutQuad function
-               val = twentytwentyEaseInOutQuad( currentTime, start, change, duration );
-               // move the document.body
-               move( val );
-               // do the animation unless its over
-               if ( currentTime < duration ) {
-                       window.requestAnimationFrame( animateScroll );
-               } else if ( callback && typeof ( callback ) === 'function' ) {
-                       // the animation is done so lets callback
-                       callback();
-               }
-       }
-       animateScroll();
-}
</del></span></pre></div>
<a id="branches53srcwpcontentthemestwentytwentystylertlcss"></a>
<div class="modfile"><h4 style="background-color: #eee; color: inherit; margin: 1em 0; padding: 1.3em; font-size: 115%">Modified: branches/5.3/src/wp-content/themes/twentytwenty/style-rtl.css</h4>
<pre class="diff"><span>
<span class="info" style="display: block; padding: 0 10px; color: #888">--- branches/5.3/src/wp-content/themes/twentytwenty/style-rtl.css     2019-12-07 11:03:09 UTC (rev 46824)
+++ branches/5.3/src/wp-content/themes/twentytwenty/style-rtl.css       2019-12-07 11:06:06 UTC (rev 46825)
</span><span class="lines" style="display: block; padding: 0 10px; color: #888">@@ -115,8 +115,15 @@
</span><span class="cx" style="display: block; padding: 0 10px"> 
</span><span class="cx" style="display: block; padding: 0 10px"> html {
</span><span class="cx" style="display: block; padding: 0 10px">        font-size: 62.5%; /* 1rem = 10px */
</span><ins style="background-color: #dfd; text-decoration:none; display:block; padding: 0 10px">+        scroll-behavior: smooth;
</ins><span class="cx" style="display: block; padding: 0 10px"> }
</span><span class="cx" style="display: block; padding: 0 10px"> 
</span><ins style="background-color: #dfd; text-decoration:none; display:block; padding: 0 10px">+@media (prefers-reduced-motion: reduce) {
+       html {
+               scroll-behavior: auto;
+       }
+}
+
</ins><span class="cx" style="display: block; padding: 0 10px"> body {
</span><span class="cx" style="display: block; padding: 0 10px">        background: #f5efe0;
</span><span class="cx" style="display: block; padding: 0 10px">        box-sizing: border-box;
</span></span></pre></div>
<a id="branches53srcwpcontentthemestwentytwentystylecss"></a>
<div class="modfile"><h4 style="background-color: #eee; color: inherit; margin: 1em 0; padding: 1.3em; font-size: 115%">Modified: branches/5.3/src/wp-content/themes/twentytwenty/style.css</h4>
<pre class="diff"><span>
<span class="info" style="display: block; padding: 0 10px; color: #888">--- branches/5.3/src/wp-content/themes/twentytwenty/style.css 2019-12-07 11:03:09 UTC (rev 46824)
+++ branches/5.3/src/wp-content/themes/twentytwenty/style.css   2019-12-07 11:06:06 UTC (rev 46825)
</span><span class="lines" style="display: block; padding: 0 10px; color: #888">@@ -115,8 +115,15 @@
</span><span class="cx" style="display: block; padding: 0 10px"> 
</span><span class="cx" style="display: block; padding: 0 10px"> html {
</span><span class="cx" style="display: block; padding: 0 10px">        font-size: 62.5%; /* 1rem = 10px */
</span><ins style="background-color: #dfd; text-decoration:none; display:block; padding: 0 10px">+        scroll-behavior: smooth;
</ins><span class="cx" style="display: block; padding: 0 10px"> }
</span><span class="cx" style="display: block; padding: 0 10px"> 
</span><ins style="background-color: #dfd; text-decoration:none; display:block; padding: 0 10px">+@media (prefers-reduced-motion: reduce) {
+       html {
+               scroll-behavior: auto;
+       }
+}
+
</ins><span class="cx" style="display: block; padding: 0 10px"> body {
</span><span class="cx" style="display: block; padding: 0 10px">        background: #f5efe0;
</span><span class="cx" style="display: block; padding: 0 10px">        box-sizing: border-box;
</span></span></pre>
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