TrackOffical/node_modules/topojson-client/src/bbox.js

import transform from "./transform.js";

export default function(topology) {
  var t = transform(topology.transform), key,
      x0 = Infinity, y0 = x0, x1 = -x0, y1 = -x0;

  function bboxPoint(p) {
    p = t(p);
    if (p[0] < x0) x0 = p[0];
    if (p[0] > x1) x1 = p[0];
    if (p[1] < y0) y0 = p[1];
    if (p[1] > y1) y1 = p[1];
  }

  function bboxGeometry(o) {
    switch (o.type) {
      case "GeometryCollection": o.geometries.forEach(bboxGeometry); break;
      case "Point": bboxPoint(o.coordinates); break;
      case "MultiPoint": o.coordinates.forEach(bboxPoint); break;
    }
  }

  topology.arcs.forEach(function(arc) {
    var i = -1, n = arc.length, p;
    while (++i < n) {
      p = t(arc[i], i);
      if (p[0] < x0) x0 = p[0];
      if (p[0] > x1) x1 = p[0];
      if (p[1] < y0) y0 = p[1];
      if (p[1] > y1) y1 = p[1];
    }
  });

  for (key in topology.objects) {
    bboxGeometry(topology.objects[key]);
  }

  return [x0, y0, x1, y1];
}