along path

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<!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="//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);

var path = svg.append("path")
    .attr("d", "m 480,200 c 100,0 0,250 100,200 100,-50 0,-250 100,-300 100,-50 350,100 100,200 -250,100 -350,100 -600,0 -250,-100 0,-250 100,-200 100,50 0,250 100,300 100,50 0,-200 100,-200");

var circle = svg.selectAll('circle')
		.data([0, 0.1])
		.enter()
      .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.
function translateAlong(path, offset) {
  var l = path.getTotalLength();
  return function(d, i, a) {
    return function(t) {
      t = (t + d) % 1;
      var p = path.getPointAtLength(t * l);
      return "translate(" + p.x + "," + p.y + ")";
    };
  };
}

</script>

https://d3js.org/d3.v4.min.js