Callbacks,promises and async/await

callbacks-vs-promises.js

const fs = require('fs') //require the filesystem module: a standard node library
const util = require('util')

// const f = fs.readFile(__dirname + '/input.txt', { encoding: 'utf8' })
// console.log('f is', f)

// process.exit()


const USER_FILENAME = __dirname + '/username.txt'

/*
//a callback hell

fs.readFile(USER_FILENAME, { encoding: 'utf8' },

    function handleResult(err, username) {
        if (err) {
            console.log('BUMMER', err.toString())
            return
        }
        console.log('GOT USERNAME FROM FILE:', username)

        fs.readFile(__dirname + `/password-${username}.txt`, { encoding: 'utf8' },

            function handleResult(err, data) {
                if (err) {
                    console.log('BUMMER', err.toString())
                    return
                }
                console.log('GOT USERNAME FROM FILE:', data)

            }
        )

    }
)

*/


/*
const successHandler = username=> {
    console.log(username)
    return $.getJSON(`/api/password-${username}`)
}
const errorHandler = console.err.bind(console)

const passwordPromise = $.getJSON('/api/username')
passwordPromise
.then(successHandler)
.catch(err=>console.error(err.toString()))

//*/



const readFileP = util.promisify(fs.readFile)

/*

//Promisified standard modules

const passwordPromise = readFileP(USER_FILENAME, { encoding: 'utf8' })
.then(username=>readFileP(__dirname + `/password-${username}.txt`, { encoding: 'utf8' }))

passwordPromise
.then(data=>console.log('PASSWORD', data))
.catch(err=>console.error(err.toString()))

*/


function readUserNameP() {
    return readFileP(USER_FILENAME, { encoding: 'utf8' })
}
function readPasswordP(username) {
    return readFileP(__dirname + `/password-${username}.txt`, { encoding: 'utf8' })
}


async function main() {
    try {
        const username = await readUserNameP()
        const password = await readPasswordP(username)
        console.log(`USER: ${username}, PASS: ${password}`)
    } catch (err) {
        console.log('BUMMER', err.toString())
        //throw new Error ('DUNNO_WHAT_HAPPENED')
    }
}

main()