Callback > Promises > Async / Await

async.js

import axios from 'axios' // for promise examples
import request from 'request' // for callback example

/**
 * Services
 */
const service = {
    getPeople: () => axios({ url: 'http://localhost:3000/people' }),
    getPlaces: () => axios({ url: 'http://localhost:3000/places' })
}

/**
 * Example #1 - Callback Hell-o
 */
function example1() {
    const obj = {}

    request.get({ url: 'http://localhost:3000/people', json: true }, (err, response, body) => {
        if (err) {
            console.error(err)
        } else {
            obj.people = body

            request.get({ url: 'http://localhost:3000/places', json: true }, (err, response, body) => {
                if (err) {
                    console.error(err)
                } else {
                    obj.places = body
                    console.log('Example #1', obj)
                }
            })
        }
    })
}

example1()

/**
 * Example #2 - Promises Alone
 */
function example2() {
    let obj = {}

    service.getPeople()
        .then(response => {
            obj.people = response.data
            return service.getPlaces()
        })
        .then(response => {
            obj.places = response.data
            console.log('Example #2', obj)
        })
        .catch(err => {
            console.log(err)
        })
}

example2()

/**
 * Example #2b - Promises with Promise.all()
 */
function example2b() {
    Promise.all([ service.getPeople(), service.getPlaces() ])
        .then(values => {
            console.log('Example #2b', values.map(v => v.data))
        })
        .catch(err => {
            console.log(err)
        })
}

example2b()

/**
 * Example #3 - Async / Await
 */
async function example3() {
    try {
        const people = await service.getPeople()
        const places = await service.getPlaces()

        console.log('Example #3', {
            people: people.data,
            places: places.data
        })
    } catch(err) {
        console.error(err)
    }
}

example3()

/**
 * Example #3b - Async / Await with Promise.all()
 */
async function example3b() {
    try {
        const values = await Promise.all([ service.getPeople(), service.getPlaces() ])
        console.log('Example #3b', values.map(v => v.data))
    } catch(err) {
        console.error(err)
    }
}

example3b()

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