Run asynchronous functions in sequence

reduce_with_asyncs.js

// Run asynchronous functions in sequence

const peopleArr  = [
    {
        username:    'glestrade',
        displayname: 'Inspector Lestrade',
        email:       '[email protected]',
        authHash:    'bdbf9920f42242defd9a7f76451f4f1d',
        lastSeen:    '2019-05-13T11:07:22+00:00',
    },
    {
        username:    'mholmes',
        displayname: 'Mycroft Holmes',
        email:       '[email protected]',
        authHash:    'b4d04ad5c4c6483cfea030ff4e7c70bc',
        lastSeen:    '2019-05-10T11:21:36+00:00',
    },
    {
        username:    'iadler',
        displayname: 'Irene Adler',
        email:       null,
        authHash:    '319d55944f13760af0a07bf24bd1de28',
        lastSeen:    '2019-05-17T11:12:12+00:00',
    },
];


function fetchMessages(username) {
    return fetch(`https://example.com/api/messages/${username}`)
        .then(response => response.json());
}

function getUsername(person) {
    return person.username;
}

async function chainedFetchMessages(p, username) {
    // In this function, p is a promise. We wait for it to finish,
    // then run fetchMessages().
    const obj  = await p;
    const data = await fetchMessages(username);
    return { ...obj, [username]: data};
}

const msgObj = peopleArr
    .map(getUsername)
    .reduce(chainedFetchMessages, Promise.resolve({}))
    .then(console.log);
// ⦘ {glestrade: [ … ], mholmes: [ … ], iadler: [ … ]}