lubien

const databaseGetUser = id =>
  id === 'not-exists'
    ? Promise.reject('some weird database error')
    : Promise.resolve({id, username: 'username'})

const databaseGetPosts = user =>
  user.id === 'fail-to-get-posts'
    ? Promise.reject('some weird database error')
    : Promise.resolve([{title: 'A'}, {title: 'B'}])

lubien

const databaseGetUser = id =>
  id === 'not-exists'
    ? Promise.reject('some weird database error')
    : Promise.resolve({id, username: 'username'})

function getUser(id) {
  return databaseGetUser(id)
    .catch(err => { throw 'user doesn\'t exists' })
}

lubien

Promise.reject('some error')
  .catch(err => { throw 'earth is not flat' })  // runs
  .catch(err => console.log(err))               // logs 'earth is not flat'

lubien

Promise.reject('some error')
  .catch(err => { throw err })  // runs
  .catch(err => console.log(2)) // runs

lubien

Promise.reject('some error')
  .catch(err => console.log(1)) // runs
  .catch(err => console.log(2)) // never runs

lubien

function someHellComputation(initialData) {
  return fnA(initialData)
    .then(fnB)
    .then(fnC)
}

someHellComputation(10)
  .then(console.log)
  .catch(err => {
    // where does err come from: fnA, fnB, fnC?

lubien

function someHellComputation(initialData) {
  return fnA(initialData)
    .then(fnB)
    .then(fnC)
}

someHellComputation(10)
  .then(console.log)
  .catch(console.error)

lubien

function someHellComputation(initialData, callback) {
  fnA(initialData, (err, intermediateData) => {
    if (err) return callback(err)

    fnB(intermediateData, (err, anotherData) => {
      if (err) return callback(err)

      fnC(anotherData), (err, finalData) => {
        if (err) return callback(err)
        callback(null, finalData)

lubien

const arr = [
  {
    id: 10,
    title: "Test 10",
    item: "Item 1"
  },
  {
    id: 10,
    title: "Test 10",
    item: "Item 2"

lubien

import lazyLoadingRoutes from '../../support/lazyLoadingRoutes'

export default lazyLoadingRoutes([
  { path: '/login', component: 'Login', meta: { requiresAuth: false } },
  { path: '/forgotPassword', component: 'ForgotPassword', meta: { requiresAuth: false } },
  { path: '/forgotEmail', component: 'ForgotEmail', meta: { requiresAuth: false } },
  { path: '/createAccount', component: 'CreateAccount', meta: { requiresAuth: false } }
])