D3 Examples - Add circle at mouse's location (2/2)

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<!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8">
  <style type="text/css">
    svg {
      background-color: #4d4d4d;
      width: 500px;
      height: 500px;
    }
    circle {
      fill: #b2182b;
    }
  </style>
</head>
<body>
  <svg></svg>
</body>
<script src="https://d3js.org/d3.v4.min.js"></script>
<script type="text/javascript">
  function mousemove() {
    d3.select("circle").remove() // Remove the previous circle. Only diffrence from block "Add circle at mouse's location (1/2)"
    var coords = d3.mouse(this);
    d3.select("svg").append("circle")
      .attr("cx", coords[0])
      .attr("cy", coords[1])
      .attr("r", 10)
  }
​
  var svg = d3.select("svg")
  svg.on("mousemove", mousemove)
</script>
</html>
    