feat: enqueue mb assets in gutenberg screens

inc/meta-box.php

@@ -110,7 +110,7 @@ protected function object_hooks() {
 	}
 
 	public function enqueue() {
-		if ( is_admin() && ! $this->is_edit_screen() ) {
+		if ( is_admin() && ! $this->is_edit_screen() && ! $this->is_gutenberg_screen() ) {
 			return;
 		}
 
@@ -149,6 +149,12 @@ public function enqueue() {
 		do_action( 'rwmb_enqueue_scripts', $this );
 	}
 
+	private function is_gutenberg_screen() : bool {
+		global $pagenow;
+
+		return in_array( $pagenow, ['site-editor.php', 'widgets.php'] );
+	}
+
 	/**
 	 * Add meta box for multiple post types
 	 */

js/validation/validation.js

@@ -216,8 +216,13 @@
 	class GutenbergValidation extends Validation {
 		init() {
 			var that = this,
-				editor = wp.data.dispatch( 'core/editor' ),
-				savePost = editor.savePost; // Reference original method.
+				editor = wp.data.dispatch( 'core/editor' );
+
+			if ( ! editor ) {
+				return false;
+			}
+
+			const savePost = editor.savePost; // Reference original method.
 
 			if ( that.settings ) {
 				that.$form.validate( that.settings );