git-history-coauthors.js

const Git = require("nodegit");

let authors = {};

Git.Repository.open(".")
  .then(function (repo) {
    // repo.getCurrentBranch, repo.getHeadCommit, repo.getMasterCommit
    return repo.getHeadCommit();
  })
  .then(function (firstCommit) {
    const history = firstCommit.history();

    history.on("end", async function (commits) {
      for await (const commit of commits) {
        var commitStats = 0;
        for (const diff of await commit.getDiff()) {
          const diffStats = await diff.getStats();
          commitStats += diffStats.insertions() + diffStats.deletions();
        }

        const author = commit.author();
        if (author in authors) {
          authors[author] += commitStats;
        } else {
          authors[author] = commitStats;
        }
      }

      // TODO: deduplicate by username and email
      for (const author of Object.keys(authors).sort(
        (author1, author2) => authors[author2] - authors[author1]
      )) {
        // sort descending
        console.log(`Co-authored-by: ${author}`);
      }
    });

    history.start();
  });