Fixed some ESM issues

Author: owen-m1

package.json

@@ -19,6 +19,7 @@
 		"build:umd": "set NODE_ENV=umd&& rollup -c build/umd-build.js",
 		"build:umd:watch": "set NODE_ENV=umd&& rollup -w -c build/umd-build.js",
 		"build:es": "set NODE_ENV=es&& rollup -c build/esm-build.js",
+		"build:es:watch": "set NODE_ENV=es&& rollup -w -c build/esm-build.js",
 		"minify": "node build/minify.js",
 		"build": "npm run build:es && npm run build:umd && npm run minify"
 	},

plugins/AutoScroll/AutoScroll.js

@@ -11,6 +11,8 @@ import {
 	getWindowScrollingElement
 } from '../../src/utils.js';
 
+import Sortable from '../../src/Sortable.js';
+
 import { Edge, IE11OrLess, Safari } from '../../src/BrowserInfo.js';
 
 let autoScrolls = [],

plugins/MultiDrag/MultiDrag.js

@@ -374,7 +374,7 @@ function MultiDragPlugin() {
 				// Do not "unfold" after around dragEl if reverted
 				if ((parentEl[expando].options.sort || parentEl !== rootEl) && multiDragElements.length > 1) {
 					let dragRect = getRect(dragEl),
-						multiDragIndex = index(dragEl, ':not(.' + Sortable.active.options.selectedClass + ')');
+						multiDragIndex = index(dragEl, ':not(.' + this.options.selectedClass + ')');
 
 					if (!initialFolding && options.animation) dragEl.thisAnimationDuration = null;
 

src/Sortable.js

@@ -1881,17 +1881,17 @@ Sortable.utils = {
  * @param  {...SortablePlugin|SortablePlugin[]} plugins       Plugins being mounted
  */
 Sortable.mount = function(...plugins) {
-		if (plugins[0].constructor === Array) plugins = plugins[0];
+	if (plugins[0].constructor === Array) plugins = plugins[0];
 
-		for (let i in plugins) {
-			let plugin = plugins[i];
-			if (!plugin.prototype || !plugin.prototype.constructor) {
-				throw `Sortable: Mounted plugin must be a constructor function, not ${ {}.toString.call(el) }`;
-			}
-			if (plugin.utils) Sortable.utils = { ...Sortable.utils, ...plugin.utils };
-
-			PluginManager.mount(plugin);
+	for (let i in plugins) {
+		let plugin = plugins[i];
+		if (!plugin.prototype || !plugin.prototype.constructor) {
+			throw `Sortable: Mounted plugin must be a constructor function, not ${ {}.toString.call(el) }`;
 		}
+		if (plugin.utils) Sortable.utils = { ...Sortable.utils, ...plugin.utils };
+
+		PluginManager.mount(plugin);
+	}
 };