gistfile1.js

const _ = require('lodash')
const faker = require('faker')

console.time('make data')

const seed = 20000

const authors = _.times(seed, n => ({
  id: 'a' + n,
  name: faker.name.findName(),
}))

const posts = _.times(seed * 10, n => ({
  id: n,
  authorId: 'a' + _.random(seed),
  title: faker.lorem.sentence(),
  context: faker.lorem.paragraph(),
}))

console.timeEnd('make data')

console.time('map posts 1')

const postsWithAuthor = posts.map(post => ({
  author: authors.find(author => author.id === post.authorId),
  ...post
}))

console.timeEnd('map posts 1')
console.log(postsWithAuthor[0])

console.time('map posts 2')

const postsWithAuthor2 = posts.map(post => ({
  author: authors[post.authorId] || authors.find(author => {
    if (author.id === post.authorId)
      return true

    authors[author.id] = author
    return false
  }),
  ...post
}))

console.timeEnd('map posts 2')
console.log(postsWithAuthor2[0])

console.time('map posts 3')

let authorsCache = {}
const postsWithAuthor3 = []

for (author of authors) {
  authorsCache[author.id] = author
}

// for (i = 0; i < posts.length; i++) {
//   const post = posts[i]
//   postsWithAuthor3[i] = {
//     author: authorsCache[post.authorId],
//     ...post // slow
//   }
// }

for (i = 0; i < posts.length; i++) {
  const post = posts[i]
  post.author = authorsCache[post.authorId]
  postsWithAuthor3[i] = post
}

console.timeEnd('map posts 3')
console.log(postsWithAuthor3[0])

gistfile2.txt

make data: 2753.530ms

map posts 1: 34069.888ms
{ author: { id: 'a13127', name: 'Gail Terry' },
  id: 0,
  authorId: 'a13127',
  title: 'Iure modi voluptates sit placeat fuga voluptatem magnam.',
  context: 'Aliquid sit maxime omnis vel laborum. Architecto quasi nesciunt dolor est iure hic facere. Possimus cum blanditiis voluptas vel nemo hic.' }

map posts 2: 432.376ms
{ author: { id: 'a13127', name: 'Gail Terry' },
  id: 0,
  authorId: 'a13127',
  title: 'Iure modi voluptates sit placeat fuga voluptatem magnam.',
  context: 'Aliquid sit maxime omnis vel laborum. Architecto quasi nesciunt dolor est iure hic facere. Possimus cum blanditiis voluptas vel nemo hic.' }

map posts 3: 85.246ms
{ id: 0,
  authorId: 'a13127',
  title: 'Iure modi voluptates sit placeat fuga voluptatem magnam.',
  context: 'Aliquid sit maxime omnis vel laborum. Architecto quasi nesciunt dolor est iure hic facere. Possimus cum blanditiis voluptas vel nemo hic.',
  author: { id: 'a13127', name: 'Gail Terry' } }

[nodemon] clean exit - waiting for changes before restart

https://stackoverflow.com/questions/5349425/whats-the-fastest-way-to-loop-through-an-array-in-javascript