beemyfriend · June 10, 2017 16:58
diff --git a/index.html b/index.html
 <!DOCTYPE html>
 <meta charset="utf-8">
 <body>
 <style>

 path {
  fill: none;
  stroke: #000;
  stroke-width: 3px;
 }

 circle {
  fill: steelblue;
  stroke: #fff;
  stroke-width: 3px;
 }

 </style>
 <script src="https://d3js.org/d3.v4.min.js"></script>
 <script>

 var points = [
  [480, 200],
  [580, 400],
  [680, 100],
  [780, 300],
  [180, 300],
  [280, 100],
  [380, 400]
 ];

 var svg = d3.select("body").append("svg")
    .attr("width", 960)
    .attr("height", 500);

 //d3v4 line generator that uses a cardinal-closed curve   
 var path = svg.append("path")
    .data([points])
    .attr("d", d3.line().curve(d3.curveCardinalClosed));

 svg.selectAll(".point")
    .data(points)
  .enter().append("circle")
    .attr("r", 4)
    .attr("transform", function(d) { return "translate(" + d + ")"; });

 var circle = svg.append("circle")
    .attr("r", 13)
    .attr("transform", "translate(" + points[0] + ")");

 transition();

 function transition() {
  circle.transition()
      .duration(10000)
      .attrTween("transform", translateAlong(path.node()))
      .on("end", transition);
 }

 // Returns an attrTween for translating along the specified path element.
 // Notice how the transition is slow for the first quarter of the aniimation
 // is fast for the second and third quarters and is slow again in the final quarter
 // This is normal behavior for d3.transition()
 function translateAlong(path) {
  var l = path.getTotalLength() * 2;
  return function(d, i, a) {
    return function(t) {
      if(t* l >= l/2){
          var p = path.getPointAtLength(l - (t*l))
      } else {
          var p = path.getPointAtLength(t * l);
      }
      return "translate(" + p.x + "," + p.y + ")";
    };
  };
 }

 </script>
	<!DOCTYPE html>
	<meta charset="utf-8">
	<body>
	<style>

	path {
	fill: none;
	stroke: #000;
	stroke-width: 3px;
	}

	circle {
	fill: steelblue;
	stroke: #fff;
	stroke-width: 3px;
	}

	</style>
	<script src="https://d3js.org/d3.v4.min.js"></script>
	<script>

	var points = [
	[480, 200],
	[580, 400],
	[680, 100],
	[780, 300],
	[180, 300],
	[280, 100],
	[380, 400]
	];

	var svg = d3.select("body").append("svg")
	.attr("width", 960)
	.attr("height", 500);

	//d3v4 line generator that uses a cardinal-closed curve
	var path = svg.append("path")
	.data([points])
	.attr("d", d3.line().curve(d3.curveCardinalClosed));

	svg.selectAll(".point")
	.data(points)
	.enter().append("circle")
	.attr("r", 4)
	.attr("transform", function(d) { return "translate(" + d + ")"; });

	var circle = svg.append("circle")
	.attr("r", 13)
	.attr("transform", "translate(" + points[0] + ")");

	transition();

	function transition() {
	circle.transition()
	.duration(10000)
	.attrTween("transform", translateAlong(path.node()))
	.on("end", transition);
	}

	// Returns an attrTween for translating along the specified path element.
	// Notice how the transition is slow for the first quarter of the aniimation
	// is fast for the second and third quarters and is slow again in the final quarter
	// This is normal behavior for d3.transition()
	function translateAlong(path) {
	var l = path.getTotalLength() * 2;
	return function(d, i, a) {
	return function(t) {
	if(t* l >= l/2){
	var p = path.getPointAtLength(l - (t*l))
	} else {
	var p = path.getPointAtLength(t * l);
	}
	return "translate(" + p.x + "," + p.y + ")";
	};
	};
	}

	</script>