index.js

getUser(1)
    .then(user => getRepositories(user.gitHubUsername))
    .then(repos => getCommits(repos[0]))
    .then(commits => console.log('Commits', commits))
    .catch(err => console.log('Error', err.message));    

console.log('Before');
async function displayCommits() {
    try {
        const user = await getUser(1);
        const repos = await getRepositories(user.gitHubUsername);
        const commit = await getCommits(repos[0]);
        console.log(commit);
    }
    catch (err) {
        console.log('Error', err.message);
    }
}
displayCommits()
console.log('After');

function getUser(id) {
    return new Promise((resolve, reject) => {
        setTimeout(() => {
            console.log('Reading a user from database...')
            resolve({ id: id, gitHubUsername: 'test' });
        }, 2000);
    });
}

function getRepositories(username) {
    return new Promise((resolve, reject) => {
        setTimeout(() => {
            console.log('Calling GitHub API...')
            resolve(['repo1', 'repo2', 'repo3']);
            reject(new Error('Could not get the repos.')); 
        }, 2000);
    });
}

function getCommits(repo) {
    return new Promise((resolve, reject) => {
        setTimeout(() => {
            console.log('Calling GitHub API...');
            resolve(['commit']);
        }, 2000);
    });
}