Formatting values

A Date renders as an ISO string out of the box. For anything else (custom number formats, nested objects), pass a format function. It receives each value and its location, and returns whatever should be encoded; return the value unchanged to pass it through.

import { stringify } from 'csv-pipe';

type Order = { id: number; total: number; placedAt: Date };

const orders: Order[] = [
  { id: 1, total: 19.5, placedAt: new Date('2026-06-04T10:00:00Z') },
  { id: 2, total: 4, placedAt: new Date('2026-06-05T12:30:00Z') }
];

stringify(orders, {
  format: (value) => (typeof value === 'number' ? value.toFixed(2) : value)
});
// id,total,placedAt
// 1.00,19.50,2026-06-04T10:00:00.000Z
// 2.00,4.00,2026-06-05T12:30:00.000Z

The hook receives a context with the column key and the row index, so you can format per column:

stringify(orders, {
  format: (value, { column }) =>
    column === 'total' && typeof value === 'number'
      ? `$${value.toFixed(2)}`
      : value
});

Non-cell values

A value that cannot be a cell (a plain object, function, symbol, or an invalid Date) throws a CsvPipeError that names the row and column. Use format to turn such values into something encodable, for example JSON.stringify.