Introduced EditorConfig#initialData. Made config param optional.

src/classiceditor.js

@@ -17,6 +17,7 @@ import ClassicEditorUIView from './classiceditoruiview';
 import getDataFromElement from '@ckeditor/ckeditor5-utils/src/dom/getdatafromelement';
 import mix from '@ckeditor/ckeditor5-utils/src/mix';
 import { isElement } from 'lodash-es';
+import CKEditorError from '@ckeditor/ckeditor5-utils/src/ckeditorerror';
 
 /**
  * The {@glink builds/guides/overview#classic-editor classic editor} implementation.
@@ -125,7 +126,8 @@ export default class ClassicEditor extends Editor {
 	 *				console.error( err.stack );
 	 *			} );
 	 *
-	 * Creating an instance when using initial data instead of a DOM element:
+	 * Creating an instance when using initial data instead of a DOM element.
+	 * The editor will then render an editable element that must be inserted into the DOM for the editor to work properly:
 	 *
 	 *		import ClassicEditor from '@ckeditor/ckeditor5-editor-classic/src/classiceditor';
 	 *		import Essentials from '@ckeditor/ckeditor5-essentials/src/essentials';
@@ -145,6 +147,19 @@ export default class ClassicEditor extends Editor {
 	 *				console.error( err.stack );
 	 *			} );
 	 *
+	 * Creating an instance on an existing DOM element using external initial content (specified in config):
+	 *
+	 *		ClassicEditor
+	 *			.create( document.querySelector( '#editor' ), {
+	 *				initialData: '<h2>Initial data</h2><p>Foo bar.</p>'
+	 *			} )
+	 *			.then( editor => {
+	 *				console.log( 'Editor was initialized', editor );
+	 *			} )
+	 *			.catch( err => {
+	 *				console.error( err.stack );
+	 *			} );
+	 *
 	 * @param {HTMLElement|String} sourceElementOrData The DOM element that will be the source for the created editor
 	 * or the editor's initial data.
 	 *
@@ -162,21 +177,26 @@ export default class ClassicEditor extends Editor {
 	 *
 	 * See the examples above to learn more.
 	 *
-	 * @param {module:core/editor/editorconfig~EditorConfig} config The editor configuration.
+	 * @param {module:core/editor/editorconfig~EditorConfig} [config] The editor configuration.
 	 * @returns {Promise} A promise resolved once the editor is ready.
 	 * The promise returns the created {@link module:editor-classic/classiceditor~ClassicEditor} instance.
 	 */
-	static create( sourceElementOrData, config ) {
+	static create( sourceElementOrData, config = {} ) {
 		return new Promise( resolve => {
 			const editor = new this( sourceElementOrData, config );
 
 			resolve(
 				editor.initPlugins()
 					.then( () => editor.ui.init( isElement( sourceElementOrData ) ? sourceElementOrData : null ) )
 					.then( () => {
-						const initialData = isElement( sourceElementOrData ) ?
-							getDataFromElement( sourceElementOrData ) :
-							sourceElementOrData;
+						if ( !isElement( sourceElementOrData ) && config.initialData ) {
+							throw new CKEditorError(
+								'editor-create-initial-data: ' +
+								'EditorConfig#initialData cannot be used together with initial data passed in Editor#create()'
+							);
+						}
+
+						const initialData = config.initialData || getInitialData( sourceElementOrData );
 
 						return editor.data.init( initialData );
 					} )
@@ -189,3 +209,7 @@ export default class ClassicEditor extends Editor {
 
 mix( ClassicEditor, DataApiMixin );
 mix( ClassicEditor, ElementApiMixin );
+
+function getInitialData( sourceElementOrData ) {
+	return isElement( sourceElementOrData ) ? getDataFromElement( sourceElementOrData ) : sourceElementOrData;
+}

tests/classiceditor.js

@@ -98,14 +98,6 @@ describe( 'ClassicEditor', () => {
 			} );
 		} );
 
-		it( 'allows to pass data to the constructor', () => {
-			return ClassicEditor.create( '<p>Hello world!</p>', {
-				plugins: [ Paragraph ]
-			} ).then( editor => {
-				expect( editor.getData() ).to.equal( '<p>Hello world!</p>' );
-			} );
-		} );
-
 		describe( 'ui', () => {
 			it( 'creates the UI using BoxedEditorUI classes', () => {
 				expect( editor.ui ).to.be.instanceof( ClassicEditorUI );
@@ -155,6 +147,49 @@ describe( 'ClassicEditor', () => {
 				} );
 		} );
 
+		it( 'should not require config object', () => {
+			// Just being safe with `builtinPlugins` static property.
+			class CustomClassicEditor extends ClassicEditor {}
+			CustomClassicEditor.builtinPlugins = [ Paragraph, Bold ];
+
+			return CustomClassicEditor.create( editorElement )
+				.then( newEditor => {
+					expect( newEditor.getData() ).to.equal( '<p><strong>foo</strong> bar</p>' );
+
+					return newEditor.destroy();
+				} );
+		} );
+
+		it( 'allows to pass data to the constructor', () => {
+			return ClassicEditor.create( '<p>Hello world!</p>', {
+				plugins: [ Paragraph ]
+			} ).then( editor => {
+				expect( editor.getData() ).to.equal( '<p>Hello world!</p>' );
+
+				editor.destroy();
+			} );
+		} );
+
+		it( 'initializes with config.initialData', () => {
+			return ClassicEditor.create( editorElement, {
+				initialData: '<p>Hello world!</p>',
+				plugins: [ Paragraph ]
+			} ).then( editor => {
+				expect( editor.getData() ).to.equal( '<p>Hello world!</p>' );
+
+				editor.destroy();
+			} );
+		} );
+
+		it( 'throws if initial data is passed in Editor#create and config.initialData is also used', done => {
+			ClassicEditor.create( '<p>Hello world!</p>', {
+				initialData: '<p>I am evil!</p>',
+				plugins: [ Paragraph ]
+			} ).catch( () => {
+				done();
+			} );
+		} );
+
 		it( 'should have undefined the #sourceElement if editor was initialized with data', () => {
 			return ClassicEditor
 				.create( '<p>Foo.</p>', {