y.js

const Node = require('./lib/node.js')
const gatherDepSet = require('./lib/gather-dep-set.js')

const tree = new Node({
  path: '/some/path',
  pkg: { name: 'root', version: '1.0.0', dependencies: { a: '', e: '' }},
  children: [
    { pkg: { name: 'a', version: '1.0.0', dependencies: { b: '', c: '' }}},
    { pkg: { name: 'b', version: '1.0.0', dependencies: { d: '' }}},
    { pkg: { name: 'c', version: '1.0.0' }},
    { pkg: { name: 'd', version: '1.0.0' }},
    { pkg: { name: 'e', version: '1.0.0', dependencies: { d: '' }}},
  ],
})

const a = tree.children.get('a')
const aSet = gatherDepSet([a], edge => edge.to !== a)
console.error([...aSet].map(n => n.name))