I am working on a task, in which I have to download a report in xlsx format. The report file is generated successfully from server, and is received on client side as well.          
        
first install these module
import * as Excel from 'exceljs';
import * as fs from 'file-saver';
In your function write these
 const workbook = new Excel.Workbook();
  var worksheet =  workbook.addWorksheet('sheet');
  worksheet.columns = [
    { header: 'Id', key: 'id', width: 10 },
    { header: 'Name', key: 'name', width: 32 }
  ];
 var buff = workbook.xlsx.writeBuffer().then(function (data) {
    var blob = new Blob([data], {type: 'application/vnd.openxmlformats-officedocument.spreadsheetml.sheet'});
    fs.saveAs(blob, "publications.xlsx");
  });
Fs is used to access file system and download file. You can also insert img https://www.npmjs.com/package/exceljs#images