List all remote git branches which have been merged into master and can be safely deleted.

list-remote-git-branches-merged-into-master.js

const chalk = require('chalk');
const execa = require('execa');
const SPLIT = '~~~~';

execa('git', [
        'for-each-ref',
        '--sort=-committerdate',
        '--sort=-authoremail',
        'refs/remotes/',
        '--merged',
        'origin/master',
        `--format="%(HEAD) %(refname:short)${SPLIT}%(objectname:short)${SPLIT}%(contents:subject)${SPLIT}%(authorname)${SPLIT}%(authoremail)${SPLIT}%(committerdate:relative)"`
    ])
    .then(getLines)
    .then(lines => lines.map(readLine))
    .then(groupByAuthor)
    .then(toArray)
    .then(writeReport);

function getLines(result) {
    return result.stdout.split('\n')
}

function readLine(line) {
    const fields = line.replace(/^"|"$/g, '').trim().split(SPLIT);
    return {
        shortRefName: fields[0].replace('origin/', ''),
        shortObjectName: fields[1],
        subject: fields[2],
        authorName: fields[3],
        authorEmail: fields[4].replace(/>|</g, ''),
        relativeCommitterDate: fields[5]
    };
}

function groupByAuthor(commits) {
    return commits.reduce(function(commitsByAuthorEmail, commit) {
        const key = commit.authorEmail.toLowerCase();
        (commitsByAuthorEmail[key] = commitsByAuthorEmail[key] || {
            authorName: commit.authorName,
            authorEmail: commit.authorEmail,
            commits: []
        });
        commitsByAuthorEmail[key].commits.push(commit);
        return commitsByAuthorEmail;
    }, {});
}

function toArray(object) {
    return Object.keys(object).map(key => object[key]);
}

function writeReport(authors) {
    authors.forEach(function(author) {
        console.log(chalk.yellow('%s %s'), author.authorName, author.authorEmail);
        console.log(chalk.grey('git push origin --delete ' + author.commits.map(commit => commit.shortRefName).join(' ')));
        console.log('');
        author.commits.forEach(function(commit) {
            console.log('    %s (%s) %s', commit.shortRefName, commit.relativeCommitterDate, chalk.grey(commit.subject));
        });
        console.log('');
    });
}

Output is something like this but in colour;

Jane Doe [email protected]
git push origin --delete issue-100 issue-96

    issue-100 (4 months ago) Add new feature to product
    issue-96 (5 months ago) Fix some bug in whatever

Jack Pipe [email protected]
git push origin --delete issue-12 issue-90

    issue-12 (3 months ago) Refactor the legacy thing
    issue-90 (5 months ago) Increase performance of core