square-transition by jermspeaks

index.html

<!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>
    // Feel free to change or delete any of the code you see in this editor!
    var svg = d3.select("body").append("svg")
      .attr("width", 960)
      .attr("height", 500)

    svg.append("path")
      .attr("fill", "none")
    	.attr("stroke", "#f0f")
    	.attr("stroke-width", 10)
    	.attr("d", "M100,100L500,400L700,300Z")
    	.transition()
    		.duration(5000)
    		.attr("d", "M200,200L600,450L50,400L500,200Z"); 

  </script>
</body>