The grid (core) · console.warn

unknown total function "{fn}"; register it in config.totalFns

Printed by The grid (core), prefixed [lattice], since 1.0.1.

Warnings reference › total:*

Identifier: total:*
Raised by: The grid (core)
Since: 1.0.1

What happened

A total, group footer or aggregation named a reduction that is neither built in nor registered. The reduction returns null, so the total renders empty rather than showing a wrong number.

The fix

Use a built-in reduction, or register yours in config.totalFns.

The smallest fix

createGrid(el, { totalFns: { median: (handle, indices) => … } });

Reference

Covered in full at the API reference.