d3.scaleOrdinal(domain, colors) gives categories fixed colors (BookNest's palette, so a book keeps its color on every chart). d3.scaleSequential(domain, interpolator) maps numbers through a d3-scale-chromatic ramp, and d3.scaleDiverging([min, mid, max], interpolator) runs two ramps away from a meaningful midpoint:
<script src="https://cdn.jsdelivr.net/npm/d3@7.9.0/dist/d3.min.js"></script>
<script src="booknest-sales.js"></script>
<svg width="620" height="96" font-family="Arial" font-size="13"></svg>
<script>
const book = d3.scaleOrdinal(SALES.books.map(b => b.key), SALES.books.map(b => b.color));
const units = d3.rollups(SALES.sales, v => d3.sum(v, d => d.units), d => d.month)
.map(d => d[1]); // 20 monthly totals
const change = units.slice(1).map((u, i) => u - units[i]); // month over month
const seq = d3.scaleSequential(d3.extent(units), d3.interpolateYlGnBu);
const m = d3.max(change, Math.abs), div = d3.scaleDiverging([-m, 0, m], d3.interpolateRdBu);
const strip = (row, label, values, fill) => {
const g = d3.select('svg').append('g').attr('transform', `translate(0, ${row * 32})`);
g.append('text').attr('y', 18).text(label);
const w = 520 / values.length;
g.selectAll('rect').data(values).join('rect').attr('height', 26).attr('fill', fill)
.attr('x', (d, i) => 90 + i * w).attr('width', w - 1);
};
strip(0, 'ordinal', book.domain(), book); strip(1, 'sequential', units, seq);
strip(2, 'diverging', change, div);
</script>
The sequential strip runs from pale (January 2025) to deep blue (December 2025); the diverging strip shows each month's change, red for a fall and blue for a rise, around a domain made symmetric by the largest change. interpolateViridis and interpolateCividis stay readable with color-vision deficiencies (Colorblind-Safe Palettes). An ordinal scale given an unexpected value adds it to its domain with the next color, unless you set unknown().
<!doctype html>
<style>
body { margin: 0; padding: 8px; background: #fafaf7; font: 12px system-ui, sans-serif; color: #263238; }
svg { width: 100%; max-width: 600px; display: block; }
</style>
<script src="https://cdn.jsdelivr.net/npm/d3@7.9.0/dist/d3.min.js"></script>
<p>Sequential interpolator: <select id="seq"><option>interpolateYlGnBu</option><option>interpolateViridis</option>
<option>interpolateCividis</option><option>interpolateOranges</option></select></p>
<svg viewBox="0 0 600 130" font-size="12"></svg>
<script>
// BookNest sample data, invented for these examples (not real sales)
const SALES = (() => {
const books = [
{ id: 1, key: 'harbor', title: 'The Quiet Harbor', author: 'Elena Marsh', genre: 'Fiction', color: '#1f5f8b', price: 18.99, rating: 4.6 },
{ id: 2, key: 'deepweb', title: 'Patterns of the Deep Web', author: 'Ravi Menon', genre: 'Technology', color: '#5b3f99', price: 39.5, rating: 4.3 },
{ id: 3, key: 'saffron', title: 'Salt and Saffron', author: 'Leila Haddad', genre: 'Cooking', color: '#e09a10', price: 24, rating: 4.8 },
{ id: 4, key: 'summit', title: 'Small Steps to Big Summits', author: 'Tom Okafor', genre: 'Self-Help', color: '#3f7d3a', price: 14.99, rating: 4.1 },
{ id: 5, key: 'clock', title: "The Clockmaker's Paradox", author: 'Iris Vale', genre: 'Science Fiction', color: '#b5452f', price: 16.2, rating: 4.5 },
{ id: 6, key: 'glass', title: 'Gardens in Glass', author: 'June Park', genre: 'Gardening', color: '#2a9d8f', price: 22.5, rating: 4.4 },
];
const units = { // units sold per month, January 2025 to August 2026
1: [40, 47, 46, 47, 57, 51, 46, 54, 60, 60, 71, 111, 52, 42, 49, 56, 59, 48, 53, 51],
2: [40, 37, 35, 41, 48, 43, 40, 42, 50, 53, 53, 84, 42, 35, 38, 41, 45, 41, 46, 46],
3: [46, 45, 41, 46, 53, 49, 46, 45, 60, 51, 63, 100, 48, 48, 49, 48, 53, 49, 48, 52],
4: [100, 80, 72, 70, 66, 66], // released March 2026
5: [48, 47, 54, 52, 65, 55, 57, 58, 64, 66, 75, 124, 58, 49, 59, 56, 63, 57, 54, 57],
6: [31, 30, 28, 35, 31, 32, 29, 30, 41, 36, 45, 64, 31, 30, 30, 38, 40, 38, 36, 38],
};
const months = d3.utcMonths(new Date('2025-01-01'), new Date('2026-09-01')).map(d3.utcFormat('%Y-%m'));
const sales = books.flatMap(b => units[b.id].map((n, i) =>
({ month: months[i + months.length - units[b.id].length], book: b.id, units: n })));
const ratings = [[4, 8, 20, 87, 293], [6, 10, 22, 95, 147], [2, 3, 8, 45, 342], [2, 3, 8, 24, 28],
[4, 8, 20, 90, 228], [4, 7, 20, 82, 147]].map((counts, i) => ({ book: i + 1, counts })); // 1 to 5 stars
const regions = [{ id: '826', name: 'United Kingdom', units: 1480 }, { id: '276', name: 'Germany', units: 1120 },
{ id: '250', name: 'France', units: 760 }, { id: '372', name: 'Ireland', units: 540 },
{ id: '528', name: 'Netherlands', units: 410 }, { id: '724', name: 'Spain', units: 320 }];
const links = [[5, 1, 38], [1, 3, 24], [2, 5, 18], [3, 6, 21], [4, 1, 12], [2, 6, 9], [4, 3, 15], [5, 6, 14]]
.map(([source, target, value]) => ({ source, target, value })); // customers who bought both
return { books, sales, ratings, regions, links };
})();
const book = d3.scaleOrdinal(SALES.books.map(b => b.key), SALES.books.map(b => b.color));
const units = d3.rollups(SALES.sales, v => d3.sum(v, d => d.units), d => d.month).map(d => d[1]);
const change = units.slice(1).map((u, i) => u - units[i]); // month over month
const m = d3.max(change, Math.abs);
const div = d3.scaleDiverging([-m, 0, m], d3.interpolateRdBu); // symmetric around 0
function strip(row, label, values, fill, text) {
const g = d3.select('svg').selectAll(`g.row${row}`).data([null]).join('g').attr('class', `row${row}`)
.attr('transform', `translate(0, ${row * 42})`);
g.selectAll('text.l').data([label]).join('text').attr('class', 'l').attr('y', 18).text(d => d);
const w = 500 / values.length;
g.selectAll('rect').data(values).join('rect').attr('height', 26).attr('fill', fill)
.attr('x', (d, i) => 90 + i * w).attr('width', w - 1)
.selectAll('title').data(d => [d]).join('title').text(text);
}
function draw() {
const seq = d3.scaleSequential(d3.extent(units), d3[d3.select('#seq').property('value')]);
strip(0, 'ordinal', book.domain(), book, d => d);
strip(1, 'sequential', units, seq, d => `${d} units`);
strip(2, 'diverging', change, div, d => `${d > 0 ? '+' : ''}${d} vs previous month`);
}
d3.select('#seq').on('change', draw);
draw();
</script>