Multi-Foci Force Layout

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

.node {
  stroke-width: 1.5px;
}

</style>
<body>
<script src="//d3js.org/d3.v3.min.js"></script>
<script>

var width = 960,
    height = 500;

var fill = d3.scale.category10();

var nodes = [],
    foci = [{x: 150, y: 150}, {x: 350, y: 250}, {x: 700, y: 400}];

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

var force = d3.layout.force()
    .nodes(nodes)
    .links([])
    .gravity(0)
    .size([width, height])
    .on("tick", tick);

var node = svg.selectAll("circle");

function tick(e) {
  var k = .1 * e.alpha;

// Push nodes toward their designated focus.
  nodes.forEach(function(o, i) {
    o.y += (foci[o.id].y - o.y) * k;
    o.x += (foci[o.id].x - o.x) * k;
  });

node
      .attr("cx", function(d) { return d.x; })
      .attr("cy", function(d) { return d.y; });
}

setInterval(function(){
  nodes.push({id: ~~(Math.random() * foci.length)});
  force.start();

node = node.data(nodes);

node.enter().append("circle")
      .attr("class", "node")
      .attr("cx", function(d) { return d.x; })
      .attr("cy", function(d) { return d.y; })
      .attr("r", 8)
      .style("fill", function(d) { return fill(d.id); })
      .style("stroke", function(d) { return d3.rgb(fill(d.id)).darker(2); })
      .call(force.drag);
}, 500);

</script>

https://d3js.org/d3.v3.min.js