index.js

const child = require("child_process");
const fs = require("fs");

const output = child
  .execSync(`git log --format=%B%H----DELIMITER----`)
  .toString("utf-8");

const commitsArray = output
  .split("----DELIMITER----\n")
  .map(commit => {
    const [message, sha] = commit.split("\n");

    return { sha, message };
  })
  .filter(commit => Boolean(commit.sha));

const currentChangelog = fs.readFileSync("./CHANGELOG.md", "utf-8");
const currentVersion = Number(require("./package.json").version);
const newVersion = currentVersion + 1;
let newChangelog = `# Version ${newVersion} (${
  new Date().toISOString().split("T")[0]
})\n\n`;

const features = [];
const chores = [];

commitsArray.forEach(commit => {
  if (commit.message.startsWith("feature: ")) {
    features.push(
      `* ${commit.message.replace("feature: ", "")} ([${commit.sha.substring(
        0,
        6
      )}](https://github.com/jackyef/changelog-generator/commit/${
        commit.sha
      }))\n`
    );
  }
  if (commit.message.startsWith("chore: ")) {
    chores.push(
      `* ${commit.message.replace("chore: ", "")} ([${commit.sha.substring(
        0,
        6
      )}](https://github.com/jackyef/changelog-generator/commit/${
        commit.sha
      }))\n`
    );
  }
});

if (features.length) {
  newChangelog += `## Features\n`;
  features.forEach(feature => {
    newChangelog += feature;
  });
  newChangelog += '\n';
}

if (chores.length) {
  newChangelog += `## Chores\n`;
  chores.forEach(chore => {
    newChangelog += chore;
  });
  newChangelog += '\n';
}

// prepend the newChangelog to the current one
fs.writeFileSync("./CHANGELOG.md", `${newChangelog}${currentChangelog}`);