Controlling What Gets Copied: Masking & Clipboard Output

What a cell shows and what it copies are two separate hooks on a policy: renderString / renderNumber decide the display, and serializeForClipboard decides what Ctrl/Cmd+C puts on the clipboard. Masking only the display is not enough — copying falls back to the raw value. This demo puts both side by side; copy the grid and paste it into the box to compare.

Select A1:F3, copy it (Ctrl/Cmd+C), and paste into the box below to see exactly what left the grid.

A1

fx

Implementation Guide

📄 View Source Code

Column	Shows	Copies	How
Email	a••••@acme.io	a••••@acme.io	renderString + serializeForClipboard
Card	•••• 1234	•••• 1234	renderString + serializeForClipboard
API key	••••••••	[redacted]	serializeForClipboard returns a placeholder
⚠ Phone	090-••••-5678	090-1234-5678	renderString only — the full value leaks on copy
Amount	$1,234.50	1234.5	renderNumber only — the default copies the raw value

Mask the display and the clipboard together

const maskCard = (value: unknown) => {
  const digits = String(value ?? '').replace(/\D/g, '');
  return digits ? `•••• ${digits.slice(-4)}` : '';
};

const CardPolicy: PolicyMixinType = {
  // What the cell shows.
  renderString: ({ value }) => maskCard(value),
  // What Ctrl/Cmd+C copies. Without this, the raw value is copied.
  serializeForClipboard: ({ point, sheet }) => maskCard(sheet.getSerializedValue({ point })),
};

Register it with useSpellbook({ policies: { card: new Policy({ mixins: [CardPolicy] }) } }) and assign it to a column with C: { policy: 'card' } in buildInitialCells.

Block copying entirely

serializeForClipboard can return anything — here a fixed placeholder, so the value never reaches the clipboard:

const SecretPolicy: PolicyMixinType = {
  renderString: ({ value }) => (value ? '••••••••' : ''),
  serializeForClipboard: () => '[redacted]',
};

The default: copy the raw value

When a policy defines no serializeForClipboard, copying uses the cell’s serialized raw value — not what is displayed. That is what you want for formatting (the Amount column copies 1234.5, which pastes cleanly into other spreadsheets), and exactly what you don’t want for a display-only mask (the ⚠ Phone column).

Limits

This controls the grid’s display and its clipboard output only. The real value is still in the sheet: it appears in the formula bar and the cell editor, and formulas, getCell and exports such as toValueMatrix return it. If a value must stay secret, don’t send it to the browser.