test.js

 class ContainerManager {

     constructor() {
         this.currentContainer = null;
         this.storedDocuments = {};
         this.attachEventListeners();
     }

     async enableContainer(container, show) {

         if (this.currentContainer !== null) {
             await this.saveContainer(this.currentContainer);
             this.currentContainer.classList.add("inactive");
         }

         container.classList.remove("inactive");
         container.innerHTML = "";
         container.appendChild(document.getElementById("mainContainer"));

         await this.replaceContainer(this.currentContainer);
         await this.loadContainer(container);

         this.currentContainer = container;

         if (show === true) {
             document.getElementById("mainContainer").style.display = "inline-block";
             document.getElementById("mainContainer").style.height = "100%";
             window.dispatchEvent(new Event('resize'));
         }
     }

     async replaceContainer(container) {
         return new Promise(resolve => {
             if (container === null) {
                 resolve(false);
             } else {
                 TXTextControl.pages.elementAt(0, page => {
                     page.getImage(TXTextControl.ImageFormat.Png, 100, 7, function (image) {
                         const img = document.createElement("img");
                         img.src = "data:image/png;base64," + image;
                         img.className = "img-thumbnail";
                         container.innerHTML = "";
                         container.appendChild(img);
                         resolve(true);
                     });
                 });
             }
         });
     }

     async saveContainer(container) {
         return new Promise(resolve => {
             if (container === null) {
                 resolve(false);
             } else {

                 var docs = this.storedDocuments;

                 TXTextControl.saveDocument(TXTextControl.StreamType.InternalUnicodeFormat, function (data) {
                     docs[container.id] = data;
                     resolve(true);
                 });
             }
         });
     }

     async loadContainer(container) {
         return new Promise(resolve => {
             if (container === null) {
                 resolve(false);
             } else {

                 console.log(this.storedDocuments[container.id]);

                 if (this.storedDocuments[container.id] !== undefined) {
                     TXTextControl.loadDocument(TXTextControl.StreamType.InternalUnicodeFormat, this.storedDocuments[container.id].data, function () {
                         resolve(true);
                     });
                 } else {
                     TXTextControl.resetContents();
                     resolve(false);
                 }
             }
         });
     }

     attachEventListeners() {
         const elements = document.getElementsByClassName("editorContainer");

         for (let i = 0; i < elements.length; i++) {
             elements[i].addEventListener("click", (elem) => {
                 if (elem.target !== this.currentContainer && elem.target.className.includes("editorContainer")) {
                     this.enableContainer(elem.target, true);
                 }
             });
         }
     }
 }

 const containerManager = new ContainerManager();