promise patterns and anti-promise patterns

quality-promises.js

// http://blog.runnable.com/post/154695425511/promise-anti-patterns
// BAD!! variable nesting

// Defining a variable to store later
var user
var accountInfo

fetchUser()
    .then((fetchedUser) => {
        // Setting the variable that we will use later
        user = fetchedUser
    })
    .then(() => {
        return fetchAccountInfo(user)
    })
    .then((fetchedAccountInfo) => {
        accountInfo = fetchedAccountInfo
    })
    .then(() => {
        // Using the variables that have been set previously
        return {
            user: user,
            accountInfo: accountInfo
        }
    })

// ALTERNATIVE GOOD VERSION

var userFetchPromise = fetchUser()
var accountInfoFetchPromise = userFetchPromise
    .then((user) => {
        return fetchAccountInfo(user)
    })
return Promise.all([userFetchPromise, accountInfoFetchPromise])
    .then((results) => {
        return {
            user: results[0],
            accountInfo: results[1]
        }
    })

// ----------------------

// Creating new promises -> BAD!!!

new Promise((resolve, reject) => {
        fetchUser().then(resolve).catch(reject)
    })
    .then((user) => {
        // Do something with user
    })

// creating new promises -> GOOD!!

fetchUser()
    .then((user) => {
        // Do something with user
    })

// ----------------------

// GOOD -> add errors

var fetchUser = (userId) => {
    return Promise.resolve()
        .then(() => {
            if (!userId) {
                throw new Error('User ID required')
            }
            return goFetchUser(userId)
        })
}

// Concurrency -> BAD!!

createDatabase()
    .then(() => {
        return insertUser()
    })
    .then(() => {
        return insertOrganization()
    })

// Concurrency -> GOOD!

createDatabase()
    .then(() => {
        return Promise.all([insertUser(), insertOrganization()])
    })

// Anonymous Functions -> BAD!!

var userFetchPromise = fetchUser()
return Promise.props({
    user: userFetchPromise,
    accountInfo: userFetchPromise.then((user) => {
        return fetchAccountInfo(user)
    })
})

// Remove anonymous functions

var userFetchPromise = fetchUser()
return Promise.props({
    user: userFetchPromise,
    accountInfo: userFetchPromise.then(fetchAccountInfo)
})