From 22ff75ac5e063b9c4cf1ed1615126fd87a93c923 Mon Sep 17 00:00:00 2001
From: Andrew Ozz <azaozz@git.wordpress.org>
Date: Sun, 28 Aug 2016 18:40:00 +0000
Subject: [PATCH] Editor: fix jumpiness on pressing backspace and delete in the
 Text editor.

Fixes #37690 for trunk.

git-svn-id: https://develop.svn.wordpress.org/trunk@38426 602fd350-edb4-49c9-b593-d223f7449a82
---
 src/wp-admin/js/editor-expand.js  | 78 ++++++++++++++++---------------
 src/wp-includes/script-loader.php |  2 +-
 2 files changed, 42 insertions(+), 38 deletions(-)

diff --git a/src/wp-admin/js/editor-expand.js b/src/wp-admin/js/editor-expand.js
index bf67c64e04..aaf34b0bb1 100644
--- a/src/wp-admin/js/editor-expand.js
+++ b/src/wp-admin/js/editor-expand.js
@@ -53,6 +53,47 @@
 				sideSortablesHeight: 0
 			};
 
+		var shrinkTextarea = window._.throttle( function() {
+			var x = window.scrollX || document.documentElement.scrollLeft;
+			var y = window.scrollY || document.documentElement.scrollTop;
+			var height = parseInt( textEditor.style.height, 10 );
+
+			textEditor.style.height = autoresizeMinHeight + 'px';
+
+			if ( textEditor.scrollHeight > autoresizeMinHeight ) {
+				textEditor.style.height = textEditor.scrollHeight + 'px';
+			}
+
+			if ( typeof x !== 'undefined' ) {
+				window.scrollTo( x, y );
+			}
+
+			if ( textEditor.scrollHeight < height ) {
+				adjust();
+			}
+		}, 300 );
+
+		function textEditorResize() {
+			var length = textEditor.value.length;
+
+			if ( mceEditor && ! mceEditor.isHidden() ) {
+				return;
+			}
+
+			if ( ! mceEditor && initialMode === 'tinymce' ) {
+				return;
+			}
+
+			if ( length < oldTextLength ) {
+				shrinkTextarea();
+			} else if ( parseInt( textEditor.style.height, 10 ) < textEditor.scrollHeight ) {
+				textEditor.style.height = Math.ceil( textEditor.scrollHeight ) + 'px';
+				adjust();
+			}
+
+			oldTextLength = length;
+		}
+
 		function getHeights() {
 			var windowWidth = $window.width();
 
@@ -75,43 +116,6 @@
 			}
 		}
 
-		function textEditorResize() {
-			if ( mceEditor && ! mceEditor.isHidden() ) {
-				return;
-			}
-
-			if ( ! mceEditor && initialMode === 'tinymce' ) {
-				return;
-			}
-
-			var length = textEditor.value.length;
-			var height = parseInt( textEditor.style.height, 10 );
-			var top = window.scrollTop;
-
-			if ( length < oldTextLength ) {
-				// textEditor.scrollHeight is not adjusted until the next line.
-				textEditor.style.height = 'auto';
-
-				if ( textEditor.scrollHeight > autoresizeMinHeight ) {
-					textEditor.style.height = textEditor.scrollHeight + 'px';
-				} else {
-					textEditor.style.height = autoresizeMinHeight + 'px';
-				}
-
-				// Prevent scroll-jumping in Firefox and IE.
-				window.scrollTop = top;
-
-				if ( textEditor.scrollHeight < height ) {
-					adjust();
-				}
-			} else if ( height < textEditor.scrollHeight ) {
-				textEditor.style.height = textEditor.scrollHeight + 'px';
-				adjust();
-			}
-
-			oldTextLength = length;
-		}
-
 		// We need to wait for TinyMCE to initialize.
 		$document.on( 'tinymce-editor-init.editor-expand', function( event, editor ) {
 			var VK = window.tinymce.util.VK,
diff --git a/src/wp-includes/script-loader.php b/src/wp-includes/script-loader.php
index 15464a17cb..b04bb9e6e4 100644
--- a/src/wp-includes/script-loader.php
+++ b/src/wp-includes/script-loader.php
@@ -554,7 +554,7 @@ function wp_default_scripts( &$scripts ) {
 			'suggestedImgAlt' => __( 'Suggested image #%d' ),
 		) );
 
-		$scripts->add( 'editor-expand', "/wp-admin/js/editor-expand$suffix.js", array( 'jquery' ), false, 1 );
+		$scripts->add( 'editor-expand', "/wp-admin/js/editor-expand$suffix.js", array( 'jquery', 'underscore' ), false, 1 );
 
 		$scripts->add( 'link', "/wp-admin/js/link$suffix.js", array( 'wp-lists', 'postbox' ), false, 1 );