Color Scale

<!DOCTYPE html>
<head>
  <meta charset="utf-8">
  <script src="https://d3js.org/d3.v5.min.js"></script>
</head>

<body>
  <script>
    var margin = {left: 20, top: 20, right: 40, bottom: 20},
        width = 950 - margin.left - margin.right,
        height = 500 - margin.top - margin.bottom;
    var svg = d3.select("body").append("svg")
      .attr("width", width + margin.left + margin.right)
      .attr("height", height + margin.top + margin.bottom)
    	.append('g')
    	.attr('transform', 'translate(' + [margin.left, margin.top] + ')');
    console.log('width', width)
    var data = [];
    for (var i=0; i<40; i++) { data.push(i) }
    
    var x = d3.scalePoint()	
    		.range([0,width])
    		.domain(data.map(d => d))
    		.padding(0.05);
    
    var rainbow = d3.scaleSequential(d3.interpolatePiYG)
    		.domain(d3.extent(data,d=>d));
    
    svg.selectAll('rect')
    	.data(data)
    	.enter().append('rect')
    	.attr('x', d => x(d))
    	.attr('y', height/2 - 50)
    	.attr('width', x.step())
    	.attr('height', 100)
    	.attr('fill', d => rainbow(d))

</script>
</body>

https://d3js.org/d3.v5.min.js