D3 Examples - Loading Circle V0

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<!DOCTYPE html>
<head>
  <meta charset="utf-8">
  <script src="https://d3js.org/d3.v4.min.js"></script>
  <style>
    body { margin:0;position:fixed;top:0;right:0;bottom:0;left:0; }
  </style>
</head>
​
<body>
  <script>
    const width = 960;
    const height = 500;
    
    const midWidth = Math.floor(width/2);
        const midHeight = Math.floor(height/2);
    
    const color = d3.scaleOrdinal(d3.schemeCategory10);
    
    let colorVar = 0;
    
    function rotateClockwise(transition) {
      transition
        .duration(5000)
        .ease(d3.easeLinear)
            .attrTween("cx", function() {
            let that = d3.select(this);
            return function(t) {
            return(midWidth + 50 * Math.cos(2 * Math.PI * t));
          }
            })
        .attrTween("cy", function() {
            let that = d3.select(this);
          return function(t) {
            return(midHeight + 50 * Math.sin(2 * Math.PI * t));
          }
        }).on("end", function() {
            d3.select(this).transition().call(rotateClockwise);
        });;
    }
       
    const svg = d3.select("body").append("svg")
        .attr("width", width)
      .attr("height", height);
​
    const circle = svg.append("circle")
      .attr("cx", midWidth)
      .attr("cy", midHeight)
        .attr("r", 20)
        .attr("fill", color(colorVar++));
    
    circle.transition().call(rotateClockwise);
  </script>
</body>
​
    