Function walk

packages/dev/parcel-packager-docs/DocsPackager.js:271–278

(obj, fn)

// cache things in pre-visit order so the references exist
const circularSymbol = Symbol('circular');
function walk(obj, fn) {
  let res = {};
  for (let k in obj) {
    res[k] = fn(obj[k], null);
  }

  return res;
}

function recurse(obj, fn) {
  if (obj[circularSymbol]) {