Zoomable Sunburst with Labels

Adapted from Mike Bostock's Zoomable Sunburst to include arc labels.

Click on any arc to zoom in. Click on the center circle to zoom out. Click on canvas background to reset zoom.

Also packaged as a reusable component at sunburst-chart.

<head>
    <style>
        body {
            font-family: Sans-serif;
            font-size: 11px;
        }

.slice {
            cursor: pointer;
        }

.slice .main-arc {
            stroke: #fff;
            stroke-width: 1px;
        }

.slice .hidden-arc {
            fill: none;
        }

.slice text {
            pointer-events: none;
            dominant-baseline: middle;
            text-anchor: middle;
        }
    </style>

const formatNumber = d3.format(',d');

const x = d3.scaleLinear()
            .range([0, 2 * Math.PI])
            .clamp(true);

const y = d3.scaleSqrt()
            .range([maxRadius*.1, maxRadius]);

const color = d3.scaleOrdinal(d3.schemeCategory20);

const partition = d3.partition();

const arc = d3.arc()
            .startAngle(d => x(d.x0))
            .endAngle(d => x(d.x1))
            .innerRadius(d => Math.max(0, y(d.y0)))
            .outerRadius(d => Math.max(0, y(d.y1)));

const middleArcLine = d => {
            const halfPi = Math.PI/2;
            const angles = [x(d.x0) - halfPi, x(d.x1) - halfPi];
            const r = Math.max(0, (y(d.y0) + y(d.y1)) / 2);

const middleAngle = (angles[1] + angles[0]) / 2;
            const invertDirection = middleAngle > 0 && middleAngle < Math.PI; // On lower quadrants write text ccw
            if (invertDirection) { angles.reverse(); }

const path = d3.path();
            path.arc(0, 0, r, angles[0], angles[1], invertDirection);
            return path.toString();
        };

const textFits = d => {
            const CHAR_SPACE = 6;

const deltaAngle = x(d.x1) - x(d.x0);
            const r = Math.max(0, (y(d.y0) + y(d.y1)) / 2);
            const perimeter = r * deltaAngle;

return d.data.name.length * CHAR_SPACE < perimeter;
        };

const svg = d3.select('body').append('svg')
            .style('width', '100vw')
            .style('height', '100vh')
            .attr('viewBox', `${-width / 2} ${-height / 2} ${width} ${height}`)
            .on('click', () => focusOn()); // Reset zoom on canvas click

d3.json('https://gist.githubusercontent.com/mbostock/4348373/raw/85f18ac90409caa5529b32156aa6e71cf985263f/flare.json', (error, root) => {
            if (error) throw error;

root = d3.hierarchy(root);
            root.sum(d => d.size);

const slice = svg.selectAll('g.slice')
                .data(partition(root).descendants());

slice.exit().remove();

const newSlice = slice.enter()
                .append('g').attr('class', 'slice')
                .on('click', d => {
                    d3.event.stopPropagation();
                    focusOn(d);
                });

newSlice.append('title')
                .text(d => d.data.name + '\n' + formatNumber(d.value));

newSlice.append('path')
                .attr('class', 'main-arc')
                .style('fill', d => color((d.children ? d : d.parent).data.name))
                .attr('d', arc);

newSlice.append('path')
                .attr('class', 'hidden-arc')
                .attr('id', (_, i) => `hiddenArc${i}`)
                .attr('d', middleArcLine);

const text = newSlice.append('text')
                .attr('display', d => textFits(d) ? null : 'none');

// Add white contour
            text.append('textPath')
                .attr('startOffset','50%')
                .attr('xlink:href', (_, i) => `#hiddenArc${i}` )
                .text(d => d.data.name)
                .style('fill', 'none')
                .style('stroke', '#fff')
                .style('stroke-width', 5)
                .style('stroke-linejoin', 'round');

text.append('textPath')
                .attr('startOffset','50%')
                .attr('xlink:href', (_, i) => `#hiddenArc${i}` )
                .text(d => d.data.name);
        });

function focusOn(d = { x0: 0, x1: 1, y0: 0, y1: 1 }) {
            // Reset to top-level if no data point specified

const transition = svg.transition()
                .duration(750)
                .tween('scale', () => {
                    const xd = d3.interpolate(x.domain(), [d.x0, d.x1]),
                        yd = d3.interpolate(y.domain(), [d.y0, 1]);
                    return t => { x.domain(xd(t)); y.domain(yd(t)); };
                });

transition.selectAll('path.main-arc')
                .attrTween('d', d => () => arc(d));

transition.selectAll('path.hidden-arc')
                .attrTween('d', d => () => middleArcLine(d));

transition.selectAll('text')
                .attrTween('display', d => () => textFits(d) ? null : 'none');

moveStackToFront(d);

function moveStackToFront(elD) {
                svg.selectAll('.slice').filter(d => d === elD)
                    .each(function(d) {
                        this.parentNode.appendChild(this);
                        if (d.parent) { moveStackToFront(d.parent); }
                    })
            }
        }
    </script>
</body>

https://d3js.org/d3.v4.min.js