Excel

A workbook built in the browser is fragile under Lightning Web Security. Use CSV or a file built on the server.

The browser file is the fragile one

Generating a spreadsheet in the browser means shipping a large script that touches APIs Lightning Web Security often blocks or distorts. A component that appears to work in a quiet trial can fail once LWS is on.

Do not plan a feature on that script. Salesforce does not support third-party libraries, and an older build is the usual reason the download breaks.

CSV

A CSV file is text. Build the string in the component, or return it from Apex, and download that. Quote any field that contains a comma, a quote, or a line break.

CSV opens in a spreadsheet application. It is enough when the reader needs rows and columns and does not need formulas or several sheets.

A file from the server

When the file must be a real workbook, build it in Apex and return it from an imperative call, or store it as a File on the record. The component starts the download. It does not assemble the workbook.

Example

javascript

function toCsv(rows) {
  return rows
    .map((row) => row.map((cell) => `"${String(cell).replaceAll('"', '""')}"`).join(','))
    .join('\n');
}