Custom radial force

function customRadial(radius, x, y) {

  var constant = function(x) {
    return function() {
      return x;
    };
  };

  var nodes,
    strength = constant(0.1),
    strengths,
    radiuses,
    xs,
    ys;

  if (typeof radius !== "function") radius = constant(+radius);
  if (typeof x !== "function") x = constant(x == null ? 0 : +x);
  if (typeof y !== "function") y = constant(y == null ? 0 : +y);

  function force(alpha) {
    for (var i = 0, n = nodes.length; i < n; ++i) {
      var node = nodes[i],
        dx = node.x - xs[i] || 1e-6,
        dy = node.y - ys[i] || 1e-6,
        r = Math.sqrt(dx * dx + dy * dy),
        k = (radiuses[i] - r) * strengths[i] * alpha / r;
      node.vx += dx * k;
      node.vy += dy * k;
    }
  }

  function initialize() {
    if (!nodes) return;
    var i, n = nodes.length;
    strengths = new Array(n);
    radiuses = new Array(n);
    xs = new Array(n);
    ys = new Array(n);
    for (i = 0; i < n; ++i) {
      radiuses[i] = +radius(nodes[i], i, nodes);
      xs[i] = +x(nodes[i], i, nodes);
      ys[i] = +y(nodes[i], i, nodes);
      strengths[i] = isNaN(radiuses[i]) ? 0 : +strength(nodes[i], i, nodes);
    }
  }

  force.initialize = function(_) {
    nodes = _, initialize();
  };

  force.strength = function(_) {
    return arguments.length ? (strength = typeof _ === "function" ? _ : constant(+_), initialize(), force) : strength;
  };

  force.radius = function(_) {
    return arguments.length ? (radius = typeof _ === "function" ? _ : constant(+_), initialize(), force) : radius;
  };

  force.x = function(_) {
    return arguments.length ? (x = typeof _ === "function" ? _ : constant(+_), initialize(), force) : x;
  };

  force.y = function(_) {
    return arguments.length ? (y = typeof _ === "function" ? _ : constant(+_), initialize(), force) : y;
  };

  return force;
}