transition

<!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width">
  <title>JS Bin</title>
</head>
<body>
  <svg height='600' width='600'></svg>
  <script src="https://cdnjs.cloudflare.com/ajax/libs/d3/4.2.3/d3.min.js">
  </script>
  <script>

    let svg = d3.select('svg');
    let circle =
        svg
          .append('circle')
          .attr('cx', 50)
          .attr('cy', 50)
          .attr('fill', 'red')
          .attr('r', 10);

  </script>

</body>
</html>