function sparkline(values, width = 64, height = 17) {
const x = d3.scaleLinear().domain([0, values.length - 1]).range([0.5, width - 0.5]);
const y = d3.scaleLinear().domain(d3.extent(values)).range([height - 0.5, 0.5]);
const context = DOM.context2d(width, height);
const line = d3.line().x((d, i) => x(i)).y(y).context(context);
context.beginPath(), line(values), context.stroke();
return context.canvas;
}