Sample for Excel - Shared with Script Lab

InsertWorkbook API Sample.yaml

name: InsertWorkbook API Sample
description: Sample for Excel
author: jipyua
host: EXCEL
api_set: {}
script:
    content: |

        $('#file').change(insertWorkbook);

        async function insertWorkbook() {
            var myFile = document.getElementById("file");
            var reader = new FileReader();
            var time1 = null;
            var time2 = null;
            var ReaderTimerStart = null;
            var readerTimerEnd = null;

            reader.onload = (function (theFile) {
                return function (e) {
                    readerTimerEnd = Date.now();
                    console.log("LoadingDoc Time: " + (readerTimerEnd - ReaderTimerStart))

                    Excel.run(function (context) {
                        
                        console.log("here")
                        var startIndex = e.target.result.indexOf("base64,");
                        var mybase64 = e.target.result.substr(startIndex + 7, e.target.result.length);
                        time1 = Date.now();
                        
                        context.workbook.worksheets.addFromBase64(mybase64);
                        return context.sync()
                            .then(function () {
                                time2 = Date.now();
                                console.log("Workbook insert Time:" + (time2 - time1) + " ms");

                            })

                    })


                };
            })(myFile.files[0]);

            // Read in the image file as a data URL.
            reader.readAsDataURL(myFile.files[0]);
            ReaderTimerStart = Date.now();



            //     app.showNotification(document.getElementById(" bro").file);
        }


        /** Default helper for invoking an action and handling errors. */
        async function tryCatch(callback) {
            try {
                await callback();
            }
            catch (error) {
                OfficeHelpers.UI.notify(error);
                OfficeHelpers.Utilities.log(error);
            }
        }
    language: typescript
template:
    content: "<form>\n\tSelect Workbook to be inserted <br> <input type=\"file\" id=\"file\">\n\t\n\n\n</form>"
    language: html
style:
    content: |
        /* Your style goes here */
    language: css
libraries: |
    https://appsforoffice.microsoft.com/lib/beta/hosted/office.js
    https://appsforoffice.microsoft.com/lib/beta/hosted/office.d.ts

    office-ui-fabric-js@1.4.0/dist/css/fabric.min.css
    office-ui-fabric-js@1.4.0/dist/css/fabric.components.min.css

    core-js@2.4.1/client/core.min.js
    @types/core-js

    @microsoft/office-js-helpers@0.7.4/dist/office.helpers.min.js
    @microsoft/office-js-helpers@0.7.4/dist/office.helpers.d.ts

    jquery@3.1.1
    @types/jquery

Hi! We tried using context.workbook.worksheets.addFromBase64(mybase64) and it gives This operation is not implemented error. We have Beta CDN for Office JS and excel-web-16.00.js. Are we missing something here?