promise-chained.js

const crypto = require('crypto'), https = require('https')
// --------------------------------------------------------------------

let setString = (str = '') => {

    return new Promise((resolve, reject) => {

        let _name = str || 'John Doe';

        try {
            resolve( _name )
        } catch (e) {
            return reject(e + '')
        }
    })
}

let getStringLength = (str) => {

    return new Promise((resolve, reject) => {

        try {
            resolve( {str: str, result: str.length} )
        } catch (e) {
            return reject(e + '')
        }
    })
}

let getStringHash = (str) => {

    return new Promise((resolve, reject) => {

        try {
            resolve({
                str: str,
                md5: crypto.createHash('md5').update(str).digest('hex'),
                sha256: crypto.createHash('sha256').update(str).digest('hex')
            })
        } catch (e) {
            return reject(e + '')
        }
    })
}

let stringBase64Encode = (str) => {

    return new Promise((resolve, reject) => {

        try {
            resolve( {str: str, base64: new Buffer(str).toString('base64')} )
        } catch (e) {
            return reject(e + '')
        }
    })
}

let stringBase64Decode = (str) => {

    return new Promise((resolve, reject) => {

        try {
            resolve( new Buffer(str, 'base64').toString('ascii') )
        } catch (e) {
            return reject(e + '')
        }
    })
}

let getTime = (timestamp) => {

    return new Promise((resolve, reject) => {

        try {

            if (timestamp === undefined || timestamp === '' || Number(timestamp) === NaN) {
                reject(new Error('Empty timestamp'))
            }

            if (Number.isNaN(Number(timestamp))) {
                reject(new Error('Invalid timestamp'))
            }

            let url = 'https://now.httpbin.org/when/' + timestamp

            https.get(url, (res) => {

                let body = '';

                res.on('data', (chunk) => { body += chunk })

                res.on('end', () => {
                    let response = JSON.parse(body)
                    resolve( response.timestamp )
                })

            }).on('error', (e) => {
                  return reject(e + '')
            })

        } catch (e) {
            return reject(e + '')
        }
    })
}

setString('username:password')
    .then((result) => {
        console.log('String: "' + result + '"')
        return result
    })
    .then(getStringLength)
    .then((result) => {
        console.log('String length: ' + result.result)
        return result.str
    })
    .then(getStringHash)
    .then((result) => {
        console.log('String MD5 hash: ' + result.md5)
        console.log('String SHA256 hash: ' + result.sha256)
        return result.str
    })
    .then(stringBase64Encode)
    .then((result) => {
        console.log('String base64 encode: ' + result.base64)
        return result.base64
    })
    .then(stringBase64Decode)
    .then((result) => {
        console.log('String base64 decode: ' + result)
    })
    .then(() => {
        let ts = (new Date()).getTime()
        return ts
    })
    .then(getTime)
    .then((result) => {
        console.log('RFC2822: ' + result.rfc2822)
        console.log('RFC3339: ' + result.rfc3339)
    })
    .catch((e) => {
        console.error(e + '')
    })

/**
 * https://www.tomas-dvorak.cz/posts/nodejs-request-without-dependencies/
 * https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error
 * https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/throw
 */

sample-output.txt

String: "username:password"
String length: 17
String MD5 hash: 133e1b8eda335c4c7f7a508620ca7f10
String SHA256 hash: bc842c31a9e54efe320d30d948be61291f3ceee4766e36ab25fa65243cd76e0e
String base64 encode: dXNlcm5hbWU6cGFzc3dvcmQ=
String base64 decode: username:password
RFC2822: Thu, 28 Dec 2017 07:36:28 GMT
RFC3339: 2017-12-28T07:36:28.00Z