Arc gradients

There is also this solution to the similar problem https://stackoverflow.com/questions/35639290/d3js-pie-chart-gradient

<!DOCTYPE html>
<head>
  <meta charset="utf-8">
  <script src="https://d3js.org/d3.v4.min.js"></script>
 <!DOCTYPE html>
<html>

<body>
    <script>
    
      let data = [25,30,40,17];
    
      let height = 750;
      let width = height;
      let radius = height * 0.4;
      let hole = radius * 0.5;
      
      let colour = d3.scaleSequential(d3.interpolatePlasma)
      
      let svg = d3.select('body')
        .append('svg')
        .attr('width', width)
        .attr('height', height)
      
      let arcFill = svg.append('g')
        .attr('transform', 'translate(' + width/2 + ',' + width/2 + ')');
      
      let arcOutline = svg.append('g')
        .attr('transform', 'translate(' + width/2 + ',' + width/2 + ')');
      
      let arc = d3.arc()
        .innerRadius(hole)
        .outerRadius(radius);
      
      let pie = d3.pie()
        .sort(null)
        .value(function(d) { return d; })
      	
      data = pie(data);

arcOutline.selectAll('.arc')
        .data(data)
        .enter()
        .append('path')
        .attr('class', 'arc')
        .attr('d', arc)
        .style('fill', function(d){
          return createGradient(d)
        })
      	.style("stroke", "white")
      	.style("stroke-width", "3px")
		
      function createGradient(d) {
        
        let miniArcs = []
        let angleExtent = d.endAngle - d.startAngle
        let noOfArcs = angleExtent * 75 //seems like a good number
        
        colour.domain([0, noOfArcs])
        let miniArcAngle = angleExtent/noOfArcs
        
        for (var j = 0; j < noOfArcs; j++) {
          let miniArc = {}
          miniArc.startAngle = d.startAngle + (miniArcAngle * j)
          //0.01 so the colours overlap slightly, so there's no funny artefacts. 
          miniArc.endAngle = miniArc.startAngle + miniArcAngle + 0.01 
          //unless it goes beyond the end of the parent arc
          miniArc.endAngle = miniArc.endAngle > d.endAngle ? d.endAngle : miniArc.endAngle
          miniArcs.push(miniArc)
        }
        
        arcFill.selectAll('.mini-arc')
          .data(miniArcs)
          .enter()
        	.append("g")
          .append('path')
          .attr('class', 'arc')
          .attr('d', arc)
        	.style("fill", function(a, i){ return colour(i) })

return "none"
        
      }
      
      
    </script>
  </body>

</html>

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