Experiment: Recursion

recursion.js

const CATEGORIES = [
  { id: 'animals', parent: null },
  { id: 'mammals', parent: 'animals' },
  { id: 'cats', parent: 'mammals' },
  { id: 'dogs', parent: 'mammals' },
  { id: 'labrador', parent: 'dogs' },
  { id: 'cocker spaniel', parent: 'dogs' },
  { id: 'rag doll', parent: 'cats' },
  { id: 'burmese', parent: 'cats' },
];

let i = 0;

const makeTree = (items, parent) => {
  let node = {};

  items
    .filter(c => c.parent === parent)
    .forEach(c => {
      console.log(i++, c.id, parent);
      node[c.id] = makeTree(items, c.id);
    });

  return node;
};

console.log(JSON.stringify(
  makeTree(CATEGORIES, null), null, 2
));


{
  "animals": {
    "mammals": {
      "cats": {
        "rag doll": {},
        "burmese": {}
      },
      "dogs": {
        "labrador": {},
        "cocker spaniel": {}
      }
    }
  }
}