check-commit-msg.js

/* eslint-disable no-console */
const fs = require('fs');
const process = require('process');
const chalk = require('chalk');

const filename = process.env['GIT_PARAMS'].split(' ')[0];
const commit_msg = fs.readFileSync(filename).toString();
const printWarning = msg => console.warn(chalk.red(msg));
const errors = [];

if(!commit_msg.match(/^GH-\d{2,4} /)) {
  errors.push('Commit messages should be prefixed with the github issue number, i.e. "GH-637 Update design of ListView"');
}

const firstLine = commit_msg.split('\n')[0];
if(firstLine.length > 60) {
  errors.push("Too long subject line in git commit message! Max 60 characters.");
}

if(errors.length){
  printWarning('Commit message policy violation(s)!\n');
  printWarning(' - ' + errors.join('\n - '));

  // https://chris.beams.io/posts/git-commit/#seven-rules
  console.log(`\nThe 7 rules of a good commit message

    1. Separate subject from body with a blank line
    2. Limit the subject line to 50 characters
    3. Capitalize the subject line
    4. Do not end the subject line with a period
    5. Use the imperative mood in the subject line
    6. Wrap the body at 72 characters
    7. Use the body to explain what and why vs. how
  `);
  console.log(chalk.green('\nYou can skip the checks using the flag `--no-verify`.'));
  process.exit(1);
}

Use with the NPM package husky and add an npm script called commitmsg with the line node scripts/check-commit-msg.js