text: export default function (x, y) {
    var nodes;
    if (x == null) x = 0;
    if (y == null) y = 0;
  
    function force() {
      var i,
          n = nodes.length,
          node,
          sx = 0,
          sy = 0;
  
      for (i = 0; i < n; ++i) {
        node = nodes[i], sx += node.x, sy += node.y;
      }
  
      for (sx = sx / n - x, sy = sy / n - y, i = 0; i < n; ++i) {
        node = nodes[i], node.x -= sx, node.y -= sy;
      }
    }
  
    force.initialize = function (_) {
      nodes = _;
    };
  
    force.x = function (_) {
      return arguments.length ? (x = +_, force) : x;
    };
  
    force.y = function (_) {
      return arguments.length ? (y = +_, force) : y;
    };
  
    return force;
  }