Async read Excel file from browser

readExcel.js

// SheetJS should be loaded (https://unpkg.com/xlsx/dist/xlsx.full.min.js)
new Promise((resolve, reject) => {
  const fileInput = document.createElement("input")
  fileInput.type='file'
  fileInput.style.display='none'
  fileInput.onchange=evt => {
    const reader = new FileReader();
    reader.readAsBinaryString(evt.target.files[0])
    reader.onload = evt2 => {
      const workbook = XLSX.read(evt2.target.result, {type: "binary"})
      console.log(workbook)
      resolve(JSON.stringify(XLSX.utils.sheet_to_json(workbook.Sheets.Raw)))
    }
  }
  document.body.appendChild(fileInput)
  fileInput.click()
})