From c5c49f47859b8faf4817d84b5ae1415ea08b4e9d Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Pawe=C5=82=20Smyrek?= <p.smyrek@cksource.com>
Date: Thu, 12 Nov 2020 12:20:31 +0100
Subject: [PATCH 1/5] Added `toArray()` helper to cast any value to an array

---
 .../src/conversion/conversion.js              |  9 +++--
 .../src/conversion/downcasthelpers.js         |  5 +--
 packages/ckeditor5-engine/src/view/element.js | 10 +++---
 .../tests/conversion/upcasthelpers.js         |  4 ++-
 .../src/image/imageinsertcommand.js           |  5 ++-
 .../src/imageupload/imageuploadcommand.js     |  5 ++-
 .../src/mediaregistry.js                      |  7 ++--
 packages/ckeditor5-table/package.json         |  2 +-
 .../src/converters/downcast.js                | 13 +++-----
 .../tests/twostepcaretmovement.js             |  6 ++--
 packages/ckeditor5-ui/src/template.js         | 11 +++----
 packages/ckeditor5-undo/tests/redocommand.js  |  3 +-
 packages/ckeditor5-undo/tests/undocommand.js  |  3 +-
 packages/ckeditor5-utils/src/locale.js        |  5 ++-
 packages/ckeditor5-utils/src/toarray.js       | 18 ++++++++++
 packages/ckeditor5-utils/tests/toarray.js     | 33 +++++++++++++++++++
 packages/ckeditor5-watchdog/package.json      |  4 +--
 .../ckeditor5-watchdog/src/contextwatchdog.js |  9 ++---
 packages/ckeditor5-widget/src/utils.js        | 10 ++----
 packages/ckeditor5-widget/tests/widget.js     |  6 ++--
 20 files changed, 100 insertions(+), 68 deletions(-)
 create mode 100644 packages/ckeditor5-utils/src/toarray.js
 create mode 100644 packages/ckeditor5-utils/tests/toarray.js

diff --git a/packages/ckeditor5-engine/src/conversion/conversion.js b/packages/ckeditor5-engine/src/conversion/conversion.js
index 9751a806698..536911d6ed6 100644
--- a/packages/ckeditor5-engine/src/conversion/conversion.js
+++ b/packages/ckeditor5-engine/src/conversion/conversion.js
@@ -10,6 +10,7 @@
 import CKEditorError from '@ckeditor/ckeditor5-utils/src/ckeditorerror';
 import UpcastHelpers from './upcasthelpers';
 import DowncastHelpers from './downcasthelpers';
+import toArray from '@ckeditor/ckeditor5-utils/src/toarray';
 
 /**
  * A utility class that helps add converters to upcast and downcast dispatchers.
@@ -74,10 +75,10 @@ export default class Conversion {
 		this._helpers = new Map();
 
 		// Define default 'downcast' & 'upcast' dispatchers groups. Those groups are always available as two-way converters needs them.
-		this._downcast = Array.isArray( downcastDispatchers ) ? downcastDispatchers : [ downcastDispatchers ];
+		this._downcast = toArray( downcastDispatchers );
 		this._createConversionHelpers( { name: 'downcast', dispatchers: this._downcast, isDowncast: true } );
 
-		this._upcast = Array.isArray( upcastDispatchers ) ? upcastDispatchers : [ upcastDispatchers ];
+		this._upcast = toArray( upcastDispatchers );
 		this._createConversionHelpers( { name: 'upcast', dispatchers: this._upcast, isDowncast: false } );
 	}
 
@@ -636,9 +637,7 @@ function* _getUpcastDefinition( model, view, upcastAlso ) {
 	yield { model, view };
 
 	if ( upcastAlso ) {
-		upcastAlso = Array.isArray( upcastAlso ) ? upcastAlso : [ upcastAlso ];
-
-		for ( const upcastAlsoItem of upcastAlso ) {
+		for ( const upcastAlsoItem of toArray( upcastAlso ) ) {
 			yield { model, view: upcastAlsoItem };
 		}
 	}
diff --git a/packages/ckeditor5-engine/src/conversion/downcasthelpers.js b/packages/ckeditor5-engine/src/conversion/downcasthelpers.js
index a3116f5aee9..6cf9338e9b3 100644
--- a/packages/ckeditor5-engine/src/conversion/downcasthelpers.js
+++ b/packages/ckeditor5-engine/src/conversion/downcasthelpers.js
@@ -19,6 +19,7 @@ import ConversionHelpers from './conversionhelpers';
 
 import { cloneDeep } from 'lodash-es';
 import CKEditorError from '@ckeditor/ckeditor5-utils/src/ckeditorerror';
+import toArray from '@ckeditor/ckeditor5-utils/src/toarray';
 
 /**
  * Downcast conversion helper functions.
@@ -1136,7 +1137,7 @@ function changeAttribute( attributeCreator ) {
 		// First remove the old attribute if there was one.
 		if ( data.attributeOldValue !== null && oldAttribute ) {
 			if ( oldAttribute.key == 'class' ) {
-				const classes = Array.isArray( oldAttribute.value ) ? oldAttribute.value : [ oldAttribute.value ];
+				const classes = toArray( oldAttribute.value );
 
 				for ( const className of classes ) {
 					viewWriter.removeClass( className, viewElement );
@@ -1155,7 +1156,7 @@ function changeAttribute( attributeCreator ) {
 		// Then set the new attribute.
 		if ( data.attributeNewValue !== null && newAttribute ) {
 			if ( newAttribute.key == 'class' ) {
-				const classes = Array.isArray( newAttribute.value ) ? newAttribute.value : [ newAttribute.value ];
+				const classes = toArray( newAttribute.value );
 
 				for ( const className of classes ) {
 					viewWriter.addClass( className, viewElement );
diff --git a/packages/ckeditor5-engine/src/view/element.js b/packages/ckeditor5-engine/src/view/element.js
index bc9d124f474..52681e38af9 100644
--- a/packages/ckeditor5-engine/src/view/element.js
+++ b/packages/ckeditor5-engine/src/view/element.js
@@ -11,6 +11,7 @@ import Node from './node';
 import Text from './text';
 import TextProxy from './textproxy';
 import toMap from '@ckeditor/ckeditor5-utils/src/tomap';
+import toArray from '@ckeditor/ckeditor5-utils/src/toarray';
 import isIterable from '@ckeditor/ckeditor5-utils/src/isiterable';
 import Matcher from './matcher';
 import StylesMap from './stylesmap';
@@ -724,8 +725,7 @@ export default class Element extends Node {
 	_addClass( className ) {
 		this._fireChange( 'attributes', this );
 
-		className = Array.isArray( className ) ? className : [ className ];
-		className.forEach( name => this._classes.add( name ) );
+		toArray( className ).forEach( name => this._classes.add( name ) );
 	}
 
 	/**
@@ -742,8 +742,7 @@ export default class Element extends Node {
 	_removeClass( className ) {
 		this._fireChange( 'attributes', this );
 
-		className = Array.isArray( className ) ? className : [ className ];
-		className.forEach( name => this._classes.delete( name ) );
+		toArray( className ).forEach( name => this._classes.delete( name ) );
 	}
 
 	/**
@@ -789,8 +788,7 @@ export default class Element extends Node {
 	_removeStyle( property ) {
 		this._fireChange( 'attributes', this );
 
-		property = Array.isArray( property ) ? property : [ property ];
-		property.forEach( name => this._styles.remove( name ) );
+		toArray( property ).forEach( name => this._styles.remove( name ) );
 	}
 
 	/**
diff --git a/packages/ckeditor5-engine/tests/conversion/upcasthelpers.js b/packages/ckeditor5-engine/tests/conversion/upcasthelpers.js
index ce1dd9de860..38c0771165c 100644
--- a/packages/ckeditor5-engine/tests/conversion/upcasthelpers.js
+++ b/packages/ckeditor5-engine/tests/conversion/upcasthelpers.js
@@ -31,6 +31,8 @@ import ViewRange from '../../src/view/range';
 import { StylesProcessor } from '../../src/view/stylesmap';
 import Writer from '../../src/model/writer';
 
+import toArray from '@ckeditor/ckeditor5-utils/src/toarray';
+
 /* globals console */
 
 describe( 'UpcastHelpers', () => {
@@ -899,7 +901,7 @@ describe( 'UpcastHelpers', () => {
 		const conversionResult = model.change( writer => upcastDispatcher.convert( viewToConvert, writer ) );
 
 		if ( markers ) {
-			markers = Array.isArray( markers ) ? markers : [ markers ];
+			markers = toArray( markers );
 
 			for ( const marker of markers ) {
 				expect( conversionResult.markers.has( marker.name ) ).to.be.true;
diff --git a/packages/ckeditor5-image/src/image/imageinsertcommand.js b/packages/ckeditor5-image/src/image/imageinsertcommand.js
index d30ca525dc1..eb8149de5ee 100644
--- a/packages/ckeditor5-image/src/image/imageinsertcommand.js
+++ b/packages/ckeditor5-image/src/image/imageinsertcommand.js
@@ -5,6 +5,7 @@
 
 import Command from '@ckeditor/ckeditor5-core/src/command';
 import { insertImage, isImageAllowed } from './utils';
+import toArray from '@ckeditor/ckeditor5-utils/src/toarray';
 
 /**
  * @module image/image/imageinsertcommand
@@ -50,9 +51,7 @@ export default class ImageInsertCommand extends Command {
 	execute( options ) {
 		const model = this.editor.model;
 
-		const sources = Array.isArray( options.source ) ? options.source : [ options.source ];
-
-		for ( const src of sources ) {
+		for ( const src of toArray( options.source ) ) {
 			insertImage( model, { src } );
 		}
 	}
diff --git a/packages/ckeditor5-image/src/imageupload/imageuploadcommand.js b/packages/ckeditor5-image/src/imageupload/imageuploadcommand.js
index d6182d64fdb..f0f383b8a23 100644
--- a/packages/ckeditor5-image/src/imageupload/imageuploadcommand.js
+++ b/packages/ckeditor5-image/src/imageupload/imageuploadcommand.js
@@ -6,6 +6,7 @@
 import FileRepository from '@ckeditor/ckeditor5-upload/src/filerepository';
 import Command from '@ckeditor/ckeditor5-core/src/command';
 import { insertImage, isImageAllowed } from '../image/utils';
+import toArray from '@ckeditor/ckeditor5-utils/src/toarray';
 
 /**
  * @module image/imageupload/imageuploadcommand
@@ -63,9 +64,7 @@ export default class ImageUploadCommand extends Command {
 
 		const fileRepository = editor.plugins.get( FileRepository );
 
-		const filesToUpload = Array.isArray( options.file ) ? options.file : [ options.file ];
-
-		for ( const file of filesToUpload ) {
+		for ( const file of toArray( options.file ) ) {
 			uploadImage( model, fileRepository, file );
 		}
 	}
diff --git a/packages/ckeditor5-media-embed/src/mediaregistry.js b/packages/ckeditor5-media-embed/src/mediaregistry.js
index 7412107c2e5..3dcf4174969 100644
--- a/packages/ckeditor5-media-embed/src/mediaregistry.js
+++ b/packages/ckeditor5-media-embed/src/mediaregistry.js
@@ -12,6 +12,7 @@ import TooltipView from '@ckeditor/ckeditor5-ui/src/tooltip/tooltipview';
 import IconView from '@ckeditor/ckeditor5-ui/src/icon/iconview';
 import Template from '@ckeditor/ckeditor5-ui/src/template';
 import { logWarning } from '@ckeditor/ckeditor5-utils/src/ckeditorerror';
+import toArray from '@ckeditor/ckeditor5-utils/src/toarray';
 
 const mediaPlaceholderIconViewBox = '0 0 64 42';
 
@@ -113,11 +114,7 @@ export default class MediaRegistry {
 
 		for ( const definition of this.providerDefinitions ) {
 			const previewRenderer = definition.html;
-			let pattern = definition.url;
-
-			if ( !Array.isArray( pattern ) ) {
-				pattern = [ pattern ];
-			}
+			const pattern = toArray( definition.url );
 
 			for ( const subPattern of pattern ) {
 				const match = this._getUrlMatches( url, subPattern );
diff --git a/packages/ckeditor5-table/package.json b/packages/ckeditor5-table/package.json
index 9f97082fb7d..5712eda2fdd 100644
--- a/packages/ckeditor5-table/package.json
+++ b/packages/ckeditor5-table/package.json
@@ -12,6 +12,7 @@
   "dependencies": {
     "@ckeditor/ckeditor5-core": "^23.1.0",
     "@ckeditor/ckeditor5-ui": "^23.1.0",
+    "@ckeditor/ckeditor5-utils": "^23.1.0",
     "@ckeditor/ckeditor5-widget": "^23.1.0",
     "lodash-es": "^4.17.15"
   },
@@ -29,7 +30,6 @@
     "@ckeditor/ckeditor5-paragraph": "^23.1.0",
     "@ckeditor/ckeditor5-typing": "^23.1.0",
     "@ckeditor/ckeditor5-undo": "^23.1.0",
-    "@ckeditor/ckeditor5-utils": "^23.1.0",
     "json-diff": "^0.5.4"
   },
   "engines": {
diff --git a/packages/ckeditor5-table/src/converters/downcast.js b/packages/ckeditor5-table/src/converters/downcast.js
index 12a535452e5..3f938248bb1 100644
--- a/packages/ckeditor5-table/src/converters/downcast.js
+++ b/packages/ckeditor5-table/src/converters/downcast.js
@@ -9,6 +9,7 @@
 
 import TableWalker from './../tablewalker';
 import { setHighlightHandling, toWidget, toWidgetEditable } from '@ckeditor/ckeditor5-widget/src/utils';
+import toArray from '@ckeditor/ckeditor5-utils/src/toarray';
 
 /**
  * Model table element to view table element conversion helper.
@@ -314,8 +315,8 @@ function renameViewTableCell( tableCell, desiredCellElementName, conversionApi )
 	setHighlightHandling(
 		renamedCell,
 		viewWriter,
-		( element, descriptor, writer ) => writer.addClass( normalizeToArray( descriptor.classes ), element ),
-		( element, descriptor, writer ) => writer.removeClass( normalizeToArray( descriptor.classes ), element )
+		( element, descriptor, writer ) => writer.addClass( toArray( descriptor.classes ), element ),
+		( element, descriptor, writer ) => writer.removeClass( toArray( descriptor.classes ), element )
 	);
 
 	viewWriter.insert( viewWriter.createPositionAfter( viewCell ), renamedCell );
@@ -363,8 +364,8 @@ function createViewTableCellElement( tableSlot, tableAttributes, insertPosition,
 		setHighlightHandling(
 			cellElement,
 			conversionApi.writer,
-			( element, descriptor, writer ) => writer.addClass( normalizeToArray( descriptor.classes ), element ),
-			( element, descriptor, writer ) => writer.removeClass( normalizeToArray( descriptor.classes ), element )
+			( element, descriptor, writer ) => writer.addClass( toArray( descriptor.classes ), element ),
+			( element, descriptor, writer ) => writer.removeClass( toArray( descriptor.classes ), element )
 		);
 	}
 
@@ -521,7 +522,3 @@ function getViewTable( viewFigure ) {
 function hasAnyAttribute( element ) {
 	return !![ ...element.getAttributeKeys() ].length;
 }
-
-function normalizeToArray( classes ) {
-	return Array.isArray( classes ) ? classes : [ classes ];
-}
diff --git a/packages/ckeditor5-typing/tests/twostepcaretmovement.js b/packages/ckeditor5-typing/tests/twostepcaretmovement.js
index 8a52f7b54dc..8ee13ad2b7c 100644
--- a/packages/ckeditor5-typing/tests/twostepcaretmovement.js
+++ b/packages/ckeditor5-typing/tests/twostepcaretmovement.js
@@ -14,6 +14,7 @@ import Position from '@ckeditor/ckeditor5-engine/src/model/position';
 import testUtils from '@ckeditor/ckeditor5-core/tests/_utils/utils';
 import { keyCodes } from '@ckeditor/ckeditor5-utils/src/keyboard';
 import { setData } from '@ckeditor/ckeditor5-engine/src/dev-utils/model';
+import toArray from '@ckeditor/ckeditor5-utils/src/toarray';
 
 import '@ckeditor/ckeditor5-core/tests/_utils/assertions/attribute';
 
@@ -963,11 +964,10 @@ describe( 'TwoStepCaretMovement()', () => {
 			else {
 				const stepIndex = scenario.indexOf( step );
 				const stepString = `in step #${ stepIndex }`;
-				let caretPosition = step.caretPosition;
 
-				if ( caretPosition !== undefined ) {
+				if ( step.caretPosition !== undefined ) {
 					// Normalize position
-					caretPosition = Array.isArray( step.caretPosition ) ? caretPosition : [ caretPosition ];
+					const caretPosition = toArray( step.caretPosition );
 					expect( selection.getFirstPosition(), `in step #${ stepIndex }, selection's first position` )
 						.to.have.deep.property( 'path', caretPosition );
 				}
diff --git a/packages/ckeditor5-ui/src/template.js b/packages/ckeditor5-ui/src/template.js
index 98db107742a..da6f275d7f3 100644
--- a/packages/ckeditor5-ui/src/template.js
+++ b/packages/ckeditor5-ui/src/template.js
@@ -16,6 +16,7 @@ import View from './view';
 import ViewCollection from './viewcollection';
 import isNode from '@ckeditor/ckeditor5-utils/src/dom/isnode';
 import { isObject, cloneDeepWith } from 'lodash-es';
+import toArray from '@ckeditor/ckeditor5-utils/src/toarray';
 
 const xhtmlNs = 'http://www.w3.org/1999/xhtml';
 
@@ -1225,7 +1226,7 @@ function normalize( def ) {
 function normalizeAttributes( attributes ) {
 	for ( const a in attributes ) {
 		if ( attributes[ a ].value ) {
-			attributes[ a ].value = [].concat( attributes[ a ].value );
+			attributes[ a ].value = toArray( attributes[ a ].value );
 		}
 
 		arrayify( attributes, a );
@@ -1290,9 +1291,7 @@ function normalizePlainTextDefinition( def ) {
 //
 // @param {module:ui/template~TemplateDefinition} def
 function normalizeTextDefinition( def ) {
-	if ( !Array.isArray( def.text ) ) {
-		def.text = [ def.text ];
-	}
+	def.text = toArray( def.text );
 }
 
 // Wraps an entry in Object in an Array, if not already one.
@@ -1312,9 +1311,7 @@ function normalizeTextDefinition( def ) {
 // @param {Object} obj
 // @param {String} key
 function arrayify( obj, key ) {
-	if ( !Array.isArray( obj[ key ] ) ) {
-		obj[ key ] = [ obj[ key ] ];
-	}
+	obj[ key ] = toArray( obj[ key ] );
 }
 
 // A helper which concatenates the value avoiding unwanted
diff --git a/packages/ckeditor5-undo/tests/redocommand.js b/packages/ckeditor5-undo/tests/redocommand.js
index a76a65fa83e..5548333a942 100644
--- a/packages/ckeditor5-undo/tests/redocommand.js
+++ b/packages/ckeditor5-undo/tests/redocommand.js
@@ -8,6 +8,7 @@ import Batch from '@ckeditor/ckeditor5-engine/src/model/batch';
 import UndoCommand from '../src/undocommand';
 import RedoCommand from '../src/redocommand';
 import { itemAt, getText } from '@ckeditor/ckeditor5-engine/tests/model/_utils/utils';
+import toArray from '@ckeditor/ckeditor5-utils/src/toarray';
 
 describe( 'RedoCommand', () => {
 	let editor, model, root, redo, undo;
@@ -28,7 +29,7 @@ describe( 'RedoCommand', () => {
 
 	describe( 'RedoCommand', () => {
 		describe( 'execute()', () => {
-			const p = pos => model.createPositionFromPath( root, [].concat( pos ) );
+			const p = pos => model.createPositionFromPath( root, toArray( pos ) );
 			const r = ( a, b ) => model.createRange( p( a ), p( b ) );
 
 			let batch0, batch1, batch2;
diff --git a/packages/ckeditor5-undo/tests/undocommand.js b/packages/ckeditor5-undo/tests/undocommand.js
index b7056590b2d..0734f526699 100644
--- a/packages/ckeditor5-undo/tests/undocommand.js
+++ b/packages/ckeditor5-undo/tests/undocommand.js
@@ -7,6 +7,7 @@ import ModelTestEditor from '@ckeditor/ckeditor5-core/tests/_utils/modeltestedit
 import Batch from '@ckeditor/ckeditor5-engine/src/model/batch';
 import UndoCommand from '../src/undocommand';
 import { itemAt, getText } from '@ckeditor/ckeditor5-engine/tests/model/_utils/utils';
+import toArray from '@ckeditor/ckeditor5-utils/src/toarray';
 
 describe( 'UndoCommand', () => {
 	let editor, model, doc, root, undo;
@@ -27,7 +28,7 @@ describe( 'UndoCommand', () => {
 	} );
 
 	describe( 'UndoCommand', () => {
-		const p = pos => model.createPositionFromPath( root, [].concat( pos ) );
+		const p = pos => model.createPositionFromPath( root, toArray( pos ) );
 		const r = ( a, b ) => model.createRange( p( a ), p( b ) );
 
 		describe( 'execute()', () => {
diff --git a/packages/ckeditor5-utils/src/locale.js b/packages/ckeditor5-utils/src/locale.js
index 6927d012912..598192e472a 100644
--- a/packages/ckeditor5-utils/src/locale.js
+++ b/packages/ckeditor5-utils/src/locale.js
@@ -9,6 +9,7 @@
 
 /* globals console */
 
+import toArray from './toarray';
 import { _translate } from './translation-service';
 
 const RTL_LANGUAGE_CODES = [ 'ar', 'fa', 'he', 'ku', 'ug' ];
@@ -153,9 +154,7 @@ export default class Locale {
 	 * @returns {String}
 	 */
 	_t( message, values = [] ) {
-		if ( !Array.isArray( values ) ) {
-			values = [ values ];
-		}
+		values = toArray( values );
 
 		if ( typeof message === 'string' ) {
 			message = { string: message };
diff --git a/packages/ckeditor5-utils/src/toarray.js b/packages/ckeditor5-utils/src/toarray.js
new file mode 100644
index 00000000000..520f68fc417
--- /dev/null
+++ b/packages/ckeditor5-utils/src/toarray.js
@@ -0,0 +1,18 @@
+/**
+ * @license Copyright (c) 2003-2020, CKSource - Frederico Knabben. All rights reserved.
+ * For licensing, see LICENSE.md or https://ckeditor.com/legal/ckeditor-oss-license
+ */
+
+/**
+ * @module utils/toarray
+ */
+
+/**
+ * Transforms any value to an array, if it is not already one. If provided value is already an array, it is returned unchanged.
+ *
+ * @param {*} [data] Value to transform to an array.
+ * @returns {Array} Array created from data.
+ */
+export default function toArray( data = [] ) {
+	return Array.isArray( data ) ? data : [ data ];
+}
diff --git a/packages/ckeditor5-utils/tests/toarray.js b/packages/ckeditor5-utils/tests/toarray.js
new file mode 100644
index 00000000000..2c8871b8f10
--- /dev/null
+++ b/packages/ckeditor5-utils/tests/toarray.js
@@ -0,0 +1,33 @@
+/**
+ * @license Copyright (c) 2003-2020, CKSource - Frederico Knabben. All rights reserved.
+ * For licensing, see LICENSE.md or https://ckeditor.com/legal/ckeditor-oss-license
+ */
+
+import toArray from '../src/toarray';
+
+describe( 'utils', () => {
+	describe( 'toArray', () => {
+		it( 'should wrap non-array values in an array', () => {
+			expect( toArray( 0 ) ).to.deep.equal( [ 0 ] );
+			expect( toArray( 1 ) ).to.deep.equal( [ 1 ] );
+			expect( toArray( '' ) ).to.deep.equal( [ '' ] );
+			expect( toArray( 'foo' ) ).to.deep.equal( [ 'foo' ] );
+			expect( toArray( false ) ).to.deep.equal( [ false ] );
+			expect( toArray( true ) ).to.deep.equal( [ true ] );
+			expect( toArray( null ) ).to.deep.equal( [ null ] );
+			expect( toArray( {} ) ).to.deep.equal( [ {} ] );
+		} );
+
+		it( 'should return array values by reference and unchanged', () => {
+			const array = toArray( [ 'foo' ] );
+
+			expect( toArray( array ) ).to.equal( array );
+			expect( toArray( array ) ).to.deep.equal( [ 'foo' ] );
+		} );
+
+		it( 'should return an empty array when no argument is given or it is `undefined`', () => {
+			expect( toArray() ).to.deep.equal( [] );
+			expect( toArray( undefined ) ).to.deep.equal( [] );
+		} );
+	} );
+} );
diff --git a/packages/ckeditor5-watchdog/package.json b/packages/ckeditor5-watchdog/package.json
index 830c8d472a9..c77737249cd 100644
--- a/packages/ckeditor5-watchdog/package.json
+++ b/packages/ckeditor5-watchdog/package.json
@@ -9,14 +9,14 @@
     "ckeditor5-lib"
   ],
   "dependencies": {
+    "@ckeditor/ckeditor5-utils": "^23.1.0",
     "lodash-es": "^4.17.15"
   },
   "devDependencies": {
     "@ckeditor/ckeditor5-core": "^23.1.0",
     "@ckeditor/ckeditor5-editor-classic": "^23.1.0",
     "@ckeditor/ckeditor5-engine": "^23.1.0",
-    "@ckeditor/ckeditor5-paragraph": "^23.1.0",
-    "@ckeditor/ckeditor5-utils": "^23.1.0"
+    "@ckeditor/ckeditor5-paragraph": "^23.1.0"
   },
   "engines": {
     "node": ">=12.0.0",
diff --git a/packages/ckeditor5-watchdog/src/contextwatchdog.js b/packages/ckeditor5-watchdog/src/contextwatchdog.js
index d93f6197192..4012c184b9a 100644
--- a/packages/ckeditor5-watchdog/src/contextwatchdog.js
+++ b/packages/ckeditor5-watchdog/src/contextwatchdog.js
@@ -13,6 +13,7 @@ import Watchdog from './watchdog';
 import EditorWatchdog from './editorwatchdog';
 import areConnectedThroughProperties from './utils/areconnectedthroughproperties';
 import getSubNodes from './utils/getsubnodes';
+import toArray from '@ckeditor/ckeditor5-utils/src/toarray';
 
 /**
  * A watchdog for the {@link module:core/context~Context} class.
@@ -234,9 +235,7 @@ export default class ContextWatchdog extends Watchdog {
 	 * @returns {Promise}
 	 */
 	add( itemConfigurationOrItemConfigurations ) {
-		const itemConfigurations = Array.isArray( itemConfigurationOrItemConfigurations ) ?
-			itemConfigurationOrItemConfigurations :
-			[ itemConfigurationOrItemConfigurations ];
+		const itemConfigurations = toArray( itemConfigurationOrItemConfigurations );
 
 		return this._actionQueue.enqueue( () => {
 			if ( this.state === 'destroyed' ) {
@@ -310,9 +309,7 @@ export default class ContextWatchdog extends Watchdog {
 	 * @returns {Promise}
 	 */
 	remove( itemIdOrItemIds ) {
-		const itemIds = Array.isArray( itemIdOrItemIds ) ?
-			itemIdOrItemIds :
-			[ itemIdOrItemIds ];
+		const itemIds = toArray( itemIdOrItemIds );
 
 		return this._actionQueue.enqueue( () => {
 			return Promise.all( itemIds.map( itemId => {
diff --git a/packages/ckeditor5-widget/src/utils.js b/packages/ckeditor5-widget/src/utils.js
index 5fd03b9034b..ba6070115af 100644
--- a/packages/ckeditor5-widget/src/utils.js
+++ b/packages/ckeditor5-widget/src/utils.js
@@ -13,6 +13,7 @@ import Rect from '@ckeditor/ckeditor5-utils/src/dom/rect';
 import BalloonPanelView from '@ckeditor/ckeditor5-ui/src/panel/balloon/balloonpanelview';
 import global from '@ckeditor/ckeditor5-utils/src/dom/global';
 import CKEditorError from '@ckeditor/ckeditor5-utils/src/ckeditorerror';
+import toArray from '@ckeditor/ckeditor5-utils/src/toarray';
 
 import dragHandleIcon from '../theme/icons/drag-handle.svg';
 import { getTypeAroundFakeCaretPosition } from './widgettypearound/utils';
@@ -124,16 +125,11 @@ export function toWidget( element, writer, options = {} ) {
 	setHighlightHandling(
 		element,
 		writer,
-		( element, descriptor, writer ) => writer.addClass( normalizeToArray( descriptor.classes ), element ),
-		( element, descriptor, writer ) => writer.removeClass( normalizeToArray( descriptor.classes ), element )
+		( element, descriptor, writer ) => writer.addClass( toArray( descriptor.classes ), element ),
+		( element, descriptor, writer ) => writer.removeClass( toArray( descriptor.classes ), element )
 	);
 
 	return element;
-
-	// Normalizes CSS class in descriptor that can be provided in form of an array or a string.
-	function normalizeToArray( classes ) {
-		return Array.isArray( classes ) ? classes : [ classes ];
-	}
 }
 
 /**
diff --git a/packages/ckeditor5-widget/tests/widget.js b/packages/ckeditor5-widget/tests/widget.js
index dc2ad1a6026..066eef7de12 100644
--- a/packages/ckeditor5-widget/tests/widget.js
+++ b/packages/ckeditor5-widget/tests/widget.js
@@ -17,6 +17,7 @@ import DomEventData from '@ckeditor/ckeditor5-engine/src/view/observer/domeventd
 import { setData as setModelData, getData as getModelData } from '@ckeditor/ckeditor5-engine/src/dev-utils/model';
 import { getData as getViewData } from '@ckeditor/ckeditor5-engine/src/dev-utils/view';
 import { keyCodes } from '@ckeditor/ckeditor5-utils/src/keyboard';
+import toArray from '@ckeditor/ckeditor5-utils/src/toarray';
 import testUtils from '@ckeditor/ckeditor5-core/tests/_utils/utils';
 
 describe( 'Widget', () => {
@@ -808,10 +809,7 @@ describe( 'Widget', () => {
 			it( name, () => {
 				testUtils.sinon.stub( editor.locale, 'contentLanguageDirection' ).value( contentLanguageDirection );
 
-				if ( !Array.isArray( actions ) ) {
-					actions = [ actions ];
-				}
-
+				actions = toArray( actions );
 				actions = actions.map( action => {
 					if ( typeof action === 'object' ) {
 						return action;

From e177695eff55c46de469dcd8bc9e892deee42d9c Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Pawe=C5=82=20Smyrek?= <p.smyrek@cksource.com>
Date: Thu, 12 Nov 2020 12:26:20 +0100
Subject: [PATCH 2/5] Simplified `_addClass()` method

---
 packages/ckeditor5-engine/src/view/element.js | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/packages/ckeditor5-engine/src/view/element.js b/packages/ckeditor5-engine/src/view/element.js
index 52681e38af9..6fb047b890f 100644
--- a/packages/ckeditor5-engine/src/view/element.js
+++ b/packages/ckeditor5-engine/src/view/element.js
@@ -725,7 +725,9 @@ export default class Element extends Node {
 	_addClass( className ) {
 		this._fireChange( 'attributes', this );
 
-		toArray( className ).forEach( name => this._classes.add( name ) );
+		for ( const name of toArray( className ) ) {
+			this._classes.add( name );
+		}
 	}
 
 	/**

From f89d200a4ec191f47b9a7088d5076fc0163d7846 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Pawe=C5=82=20Smyrek?= <p.smyrek@cksource.com>
Date: Thu, 12 Nov 2020 12:30:08 +0100
Subject: [PATCH 3/5] Simplified `_removeClass()` and `_removeStyle()` methods

---
 packages/ckeditor5-engine/src/view/element.js | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/packages/ckeditor5-engine/src/view/element.js b/packages/ckeditor5-engine/src/view/element.js
index 6fb047b890f..4967b09294d 100644
--- a/packages/ckeditor5-engine/src/view/element.js
+++ b/packages/ckeditor5-engine/src/view/element.js
@@ -744,7 +744,9 @@ export default class Element extends Node {
 	_removeClass( className ) {
 		this._fireChange( 'attributes', this );
 
-		toArray( className ).forEach( name => this._classes.delete( name ) );
+		for ( const name of toArray( className ) ) {
+			this._classes.delete( name );
+		}
 	}
 
 	/**
@@ -790,7 +792,9 @@ export default class Element extends Node {
 	_removeStyle( property ) {
 		this._fireChange( 'attributes', this );
 
-		toArray( property ).forEach( name => this._styles.remove( name ) );
+		for ( const name of toArray( property ) ) {
+			this._styles.remove( name );
+		}
 	}
 
 	/**

From 2627e7a213ae8828cc5443feba5cc26adba1d194 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Pawe=C5=82=20Smyrek?= <p.smyrek@cksource.com>
Date: Thu, 19 Nov 2020 10:43:09 +0100
Subject: [PATCH 4/5] Default value in toArray() is not needed

---
 packages/ckeditor5-utils/src/toarray.js   | 4 ++--
 packages/ckeditor5-utils/tests/toarray.js | 6 +-----
 2 files changed, 3 insertions(+), 7 deletions(-)

diff --git a/packages/ckeditor5-utils/src/toarray.js b/packages/ckeditor5-utils/src/toarray.js
index 520f68fc417..641b680c019 100644
--- a/packages/ckeditor5-utils/src/toarray.js
+++ b/packages/ckeditor5-utils/src/toarray.js
@@ -10,9 +10,9 @@
 /**
  * Transforms any value to an array, if it is not already one. If provided value is already an array, it is returned unchanged.
  *
- * @param {*} [data] Value to transform to an array.
+ * @param {*} data Value to transform to an array.
  * @returns {Array} Array created from data.
  */
-export default function toArray( data = [] ) {
+export default function toArray( data ) {
 	return Array.isArray( data ) ? data : [ data ];
 }
diff --git a/packages/ckeditor5-utils/tests/toarray.js b/packages/ckeditor5-utils/tests/toarray.js
index 2c8871b8f10..f0c84138641 100644
--- a/packages/ckeditor5-utils/tests/toarray.js
+++ b/packages/ckeditor5-utils/tests/toarray.js
@@ -16,6 +16,7 @@ describe( 'utils', () => {
 			expect( toArray( true ) ).to.deep.equal( [ true ] );
 			expect( toArray( null ) ).to.deep.equal( [ null ] );
 			expect( toArray( {} ) ).to.deep.equal( [ {} ] );
+			expect( toArray() ).to.deep.equal( [ undefined ] );
 		} );
 
 		it( 'should return array values by reference and unchanged', () => {
@@ -24,10 +25,5 @@ describe( 'utils', () => {
 			expect( toArray( array ) ).to.equal( array );
 			expect( toArray( array ) ).to.deep.equal( [ 'foo' ] );
 		} );
-
-		it( 'should return an empty array when no argument is given or it is `undefined`', () => {
-			expect( toArray() ).to.deep.equal( [] );
-			expect( toArray( undefined ) ).to.deep.equal( [] );
-		} );
 	} );
 } );

From 81c10ea10bdbfbdc02e8ffd38523fade5750b5a8 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Pawe=C5=82=20Smyrek?= <p.smyrek@cksource.com>
Date: Thu, 19 Nov 2020 10:44:33 +0100
Subject: [PATCH 5/5] Improved description

---
 packages/ckeditor5-utils/src/toarray.js | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/packages/ckeditor5-utils/src/toarray.js b/packages/ckeditor5-utils/src/toarray.js
index 641b680c019..171de7b0b9c 100644
--- a/packages/ckeditor5-utils/src/toarray.js
+++ b/packages/ckeditor5-utils/src/toarray.js
@@ -8,7 +8,7 @@
  */
 
 /**
- * Transforms any value to an array, if it is not already one. If provided value is already an array, it is returned unchanged.
+ * Transforms any value to an array. If the provided value is already an array, it is returned unchanged.
  *
  * @param {*} data Value to transform to an array.
  * @returns {Array} Array created from data.