小编Emh*_*vek的帖子

我想了解以下示例，因此对我来说很清楚。不幸的是，我的头挂在了线上：.forEach（c =>（node [c.id] = makeTree（categories，c.id）））。有人可以给我提示吗？

let categories = [
  { id: 'animals', parent: null },
  { id: 'mammals', parent: 'animals' },
  { id: 'cats', parent: 'mammals' },
  { id: 'dogs', parent: 'mammals' },
  { id: 'chihuahua', parent: 'dogs' },
  { id: 'labrador', parent: 'dogs' },
  { id: 'persian', parent: 'cats' },
  { id: 'siamese', parent: 'cats' }
];

let makeTree = (categories, parent) => {
  let node = {};
  categories
    .filter(c => c.parent == parent)
    .forEach(c => (node[c.id] = makeTree(categories, …