11-fs-async.js

const { readFile, writeFile } = require('fs')
console.log('start')
readFile('./content/first.txt', 'utf8', (err, result) => {
    if (err) {
        console.log(err)
        return
    }
    const first = result;
    readFile('./content/second.txt', 'utf8', (err, result) => {
        if (err) {
            console.log(err)
            return
        }
        const second = result;
        writeFile('./content/result-async.txt',
            `Here is the result : ${first},${second}`,
            (err, result) => {
            if (err) {
                console.log(err)
                return
            }
            console.log('Done with this task')
        }
        )
})
})
console.log('Starting next tasks')