Old-way is better this case;

src/util/LoopController.js

@@ -1,71 +1,107 @@
-let loopIsActive = false;
-let animationFrame = null;
-const loopRegister = [];
-
-class LoopController
-{
-    constructor() {
-        this.rafStep = this.rafStep.bind(this);
-    }
-
-    getRegisteredItems() {
-        return [...loopRegister];
-    }
-
-    registerScrollbar(scrollbar) {
-        if (!loopRegister.includes(scrollbar)) {
-            loopRegister.push(scrollbar);
-
-            this.start();
+function LoopControllerClass() {
+    /**
+     * @typedef {Object} Scrollbar
+     * @property {function} update
+     */
+
+    /**
+     * @type {Scrollbar[]}
+     */
+    const scrollbarsRegister = [];
+
+    /**
+     * true if loop is active
+     * @type {boolean}
+     */
+    let isActive = false;
+    /**
+     * ID of requested animation frame
+     * @type {null|number}
+     */
+    let animationFrameId = null;
+
+    /**
+     * Function that called in animation frame
+     */
+    const animationFrameCallback = () => {
+        if (!isActive) {return;}
+
+        for (let scrollbar of scrollbarsRegister) {
+            scrollbar.update();
         }
 
-        return this;
+        requestAnimationFrame(animationFrameCallback);
     };
 
-    unregisterScrollbar(scrollbar) {
-        let index = loopRegister.indexOf(scrollbar);
+    /**
+     * Stop the loop if it wasn't active
+     * @return {LoopControllerClass}
+     */
+    this.start = () => {
+        if (isActive) {return this;}
 
-        if (index !== -1) {
-            loopRegister.length === 1 && this.stop();
+        isActive = true;
 
-            loopRegister.splice(index, 1);
-        }
-
-        return this;
+        animationFrameId && cancelAnimationFrame(animationFrameId);
+        requestAnimationFrame(animationFrameCallback);
     };
+    /**
+     * Stop the loop if it is active
+     * @return {LoopControllerClass}
+     */
+    this.stop = () => {
+        if (!isActive) {return this;}
 
-    start() {
-        if (!loopIsActive) {
-            loopIsActive = true;
+        isActive = false;
 
-            animationFrame && cancelAnimationFrame(animationFrame);
-            animationFrame = requestAnimationFrame(this.rafStep);
-        }
-
-        return this;
+        animationFrameId && cancelAnimationFrame(animationFrameId);
+        animationFrameId = null;
     };
 
-    rafStep() {
-        if (!loopIsActive) {return;}
+    /**
+     * Return the array pf registered scrollbars
+     * @return {Scrollbar[]}
+     */
+    this.getRegisteredScrollbars = () => {
+        return [...scrollbarsRegister];
+    };
+    /**
+     * Add the scrollbar to list to iterate each loop
+     * @param {Scrollbar} scrollbar
+     * @return {LoopControllerClass}
+     */
+    this.registerScrollbar = (scrollbar) => {
+        if (scrollbarsRegister.indexOf(scrollbar) === -1) {
+            scrollbarsRegister.push(scrollbar);
 
-        for (let i = 0; i < loopRegister.length; i++) {
-            loopRegister[i].update();
+            this.start();
         }
 
-        animationFrame = requestAnimationFrame(this.rafStep);
+        return this;
     };
+    /**
+     * Remove the scrollbar from list to iterate each loop
+     * @param {Scrollbar} scrollbar
+     * @return {LoopControllerClass}
+     */
+    this.unregisterScrollbar = (scrollbar) => {
+        const index = scrollbarsRegister.indexOf(scrollbar);
 
-    stop() {
-        if (loopIsActive) {
-            loopIsActive = false;
-
-            animationFrame && cancelAnimationFrame(animationFrame);
+        if (index !== -1) {
+            scrollbarsRegister.splice(index, 1);
         }
 
         return this;
     };
 }
 
-const instance = new LoopController();
+export const LoopController = new LoopControllerClass();
+export default LoopController;
 
-export default instance;
+/**
+ * Return new instance of LoopControllerClass
+ * @return {LoopControllerClass}
+ */
+export function createLoopController() {
+    return new LoopControllerClass();
+}

tests/LoopController.spec.js

@@ -1,7 +1,7 @@
-import expect         from "expect";
-import React          from "react";
-import sinon          from 'sinon';
-import LoopController from '../src/util/LoopController';
+import expect                                   from "expect";
+import React                                    from "react";
+import sinon                                    from 'sinon';
+import { createLoopController, LoopController } from '../src/util/LoopController';
 
 describe("LoopController", () => {
     const ScrollbarMock = {
@@ -12,17 +12,18 @@ describe("LoopController", () => {
 
     it("should register the scrollbar", () => {
         LoopController.registerScrollbar(ScrollbarMock);
-        expect(LoopController.getRegisteredItems().length).toEqual(1);
+        expect(LoopController.getRegisteredScrollbars().length).toEqual(1);
+        expect(LoopController.getRegisteredScrollbars()[0]).toEqual(ScrollbarMock);
     });
 
     it("should call an 'update' method of registered scrollbar", (done) => {
         setTimeout(() => {
-            expect(spy.callCount).toBeGreaterThan(10);
+            expect(spy.callCount).toBeGreaterThanOrEqual(30);
             done();
         }, 500);
     });
 
-    it("should call stop the loop when .stop() executed", (done) => {
+    it("should stop the loop when .stop() executed", (done) => {
         let callCount = spy.callCount * 1;
         LoopController.stop();
 
@@ -32,7 +33,7 @@ describe("LoopController", () => {
         }, 500);
     });
 
-    it("should call start the loop when .start() executed", (done) => {
+    it("should start the loop when .start() executed", (done) => {
         let callCount = spy.callCount * 1;
         LoopController.start();
 
@@ -44,6 +45,10 @@ describe("LoopController", () => {
 
     it("should unregister the scrollbar", () => {
         LoopController.unregisterScrollbar(ScrollbarMock);
-        expect(LoopController.getRegisteredItems().length).toEqual(0);
+        expect(LoopController.getRegisteredScrollbars().length).toEqual(0);
+    });
+
+    it("createLoopController should return new controller", () => {
+        expect(createLoopController()).not.toEqual(LoopController);
     });
 });