demo D128
Formula entry
A spreadsheet formula typed into a cell, and the evaluator reach limit
formulaFunctions
The configuration
<script>
import { createGrid } from 'https://cdn.jsdelivr.net/npm/@toclocoinc/lattice-grid@1.27.0/lattice-grid.esm.min.js';
import createLatticeAction from 'https://cdn.jsdelivr.net/npm/@toclocoinc/lattice-grid@1.27.0/modules/svelte.esm.min.js';
const lattice = createLatticeAction({ createGrid });
const config = {
rowKey: 'id',
edit: true,
selection: 'multiple',
columns: [
{ field: 'description', title: 'Description', layout: { flex: 1, min: 160, pin: 'start' } },
{ field: 'quantity', title: 'Qty', type: 'number', edit: true, layout: { width: 100 } },
{ field: 'unitPrice', title: 'Unit price', type: 'number', edit: true,
format: { style: 'currency', currency: 'GBP' }, layout: { width: 140 } },
{ field: 'discount', title: 'Discount', type: 'number', edit: true,
format: { style: 'percent', decimals: 0 }, layout: { width: 140 } },
{ id: 'lineNet', title: 'Line net', type: 'number',
format: { style: 'currency', currency: 'GBP' }, layout: { width: 130 },
value: {
deps: ['quantity', 'unitPrice', 'discount'],
compute: (d) => d.quantity * d.unitPrice * (1 - d.discount),
} },
{ field: 'total', title: 'Total', type: 'number',
format: { style: 'currency', currency: 'GBP' },
layout: { width: 140, pin: 'end' }, total: 'sum',
// A text editor on a number column lets a reader type a formula such as
// =ROUND(quantity * unitPrice * (1 - discount), 2). It is worked out from
// this row's fields and a closed library of functions, with no eval
// behind it. The default number editor takes a number instead, so a
// column that accepts formulas asks for the text editor here.
edit: { enabled: true, editor: 'text' } },
],
rows, // invoice lines: description, quantity, unitPrice, discount, total (empty)
};
</script>
<svelte:head>
<link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/@toclocoinc/lattice-grid@1.27.0/lattice-grid.min.css">
</svelte:head>
<div use:lattice={config} style="height: 540px"></div>Typing a spreadsheet formula into a cell
Formula entry lets a cell hold =SUM(B2:B8) or =A3*1.2 instead of a static value, and the grid parses, evaluates, and re-evaluates it as the referenced cells change. A developer reaches for it wherever a grid stands in for a spreadsheet a user already expects to type into: budget lines, pricing sheets, a reconciliation view where a total needs to track its inputs rather than be pasted in by hand. Lattice Grid registers the supported operators and functions through formulaFunctions, so a column can expose only SUM, AVERAGE, and a handful of arithmetic operators, or a wider set, without the evaluator accepting an unbounded expression language. Entry works like inline editing: a formula is typed directly into the cell, committed with Enter, and re-parsed each time a dependency’s value is written. Lattice Grid tracks a bounded evaluator reach, so a formula referencing thousands of cells fails predictably at the configured limit rather than recursing until the tab stalls, which matters for a JavaScript data grid rendering tens of thousands of rows where a runaway calculation would otherwise block the main thread. A screen reader announces the evaluated result, not the formula text, so a non-sighted user hears the number a sighted user sees, with the formula itself available on request when the cell is focused for editing.
How do I add spreadsheet formulas to a grid cell?
Configure the column’s formulaFunctions with the operators and functions a formula is allowed to call, then enter a formula in a cell starting with =. Lattice Grid parses it, evaluates it against the referenced cells, and re-evaluates it whenever those cells change. An evaluator reach limit caps how many dependencies a single formula can walk, so a malformed or excessive reference fails at that boundary rather than degrading performance across the grid.