Insert a web-hosted Excel file into current workbook by using Excel JavaScript API

I try to insert an external Excel workbook (including all related worksheets). The file is accessible by url like https://www.excel.com/template.xlsx

However I'm stuck right now. I don't find any documentation how I could achieve this. The only doc I've found is about using the file picker: https://learn.microsoft.com/en-us/javascript/api/excel/excel.workbook?view=excel-js-preview#excel-excel-workbook-insertworksheetsfrombase64-member(1)

This works but that's not the solution I need. I changed the code, that the script downloads the file as blob creates a new file and use the recommended FileReader. But still no success. This is my code so far:

export async function downloadAndImportTemplate() {
const templateFileUrl: string = "https://www.test.com/template.xlsx";
try {
  // Fetch the workbook from server
  const response = await fetch(templateFileUrl);
  const workbookBlob = await response.blob();

// Create a File object
const fileName = "template.xlsx"; 
const excelFile: File = new File([workbookBlob], fileName, { type: workbookBlob.type });

// Use FileReader to read the fetched workbook
const templateFileReader: FileReader = new FileReader();
templateFileReader.onload = (event) => {
  Excel.run((context) => {
    // Remove the metadata before the base64-encoded string.
    let startIndex: number = templateFileReader.result.toString().indexOf("base64,");
    const externalWorkbook: string = templateFileReader.result.toString().substring(startIndex + 7);

    // Use Excel JS API to insert the workbook content
    const currentWorkbook = context.workbook;
    currentWorkbook.insertWorksheetsFromBase64(externalWorkbook);
    return context.sync();
  });
};

templateFileReader.readAsArrayBuffer(excelFile);
} catch (error) {
textError.textContent = error;
}
}

Thanks for any advice

Ok got it. Missed it to read the data as data url. That's my working solution now:

export async function downloadAndImportTemplate() {
const templateFileUrl: string = "https://test.com/template.xlsx";

try {
// Fetch the workbook from your server
const response = await fetch(templateFileUrl);
const workbookBlob = await response.blob();
// Create a File object
const fileName = "template.xlsx"; // Provide a filename for the File object
const excelFile: File = new File([workbookBlob], fileName, { type: workbookBlob.type });

// Use FileReader to read the fetched workbook
const templateFileReader: FileReader = new FileReader();
templateFileReader.onload = (event) => {
  Excel.run((context) => {
    // Remove the metadata before the base64-encoded string.
    let startIndex: number = templateFileReader.result.toString().indexOf("base64,");
    const templateWorkbook: string = templateFileReader.result.toString().substring(startIndex + 7);

    // Set up the insert options.
    let options = {
      sheetNamesToInsert: [], // Insert all the worksheets from the source workbook.
      positionType: Excel.WorksheetPositionType.end, // Insert after the `relativeTo` sheet.

    // Use Excel JS API to insert the workbook content
    const currentWorkbook = context.workbook;
    currentWorkbook.insertWorksheetsFromBase64(templateWorkbook, options);
    return context.sync();
  });
};
templateFileReader.readAsDataURL(excelFile);
} catch (error) {
textError.textContent = error;
}
}