Utility to checkout a remote fork and branch from a GitHub PR

git-fork.js

#!/usr/bin/env node

'use strict';

const { exec, execSync } = require('child_process');

const args = process.argv[0] === 'node'
  ? process.argv.slice(1)
  : process.argv.slice(2);

const firstArg = args[0];

if (firstArg === '--help' || firstArg === '-h') {
  console.log('Quickly checkout a Git branch from a fork.')
  console.log("\x1b[2m", '\n  # Short hand format; paste string from GitHub PR copy button:', "\x1b[0m");
  console.log('  git-fork username:branch-name');
  console.log("\x1b[2m", '\n  # Long hand format; specify user, repo, and (optionally) branch name:', "\x1b[0m");
  console.log('  git-fork username repo [optional-branch-name]');
  process.exit(0);
}

let user, repo, branch;
if (firstArg.includes(':')) {
  // Shorthand from clicking GitHub's copy button.
  // e.g. "username:branch-name"

  let result = firstArg.split(':');
  user = result[0];
  branch = result[1];

  result = execSync('git config --get remote.origin.url').toString();
  result = result.match(/\/(.+)\.git/);
  repo = result[1];
} else {
  // Long form.
  // e.g. "git-fork user repo optional-branch"
  user = args[0];
  repo = args[1];
  branch = args[2];
}

function noop() {}

async function logAndExec(command) {
  console.log(command);

  return new Promise((resolve, reject) =>
    exec(command, error => {
      if (!error) {
        resolve();
      } else {
        reject(error);
      }
    })
  );
}

async function main() {
  try {
    await logAndExec(`git remote add ${user} git@github.com:${user}/${repo}.git`);
  } catch (error) {
    if (!error.message.includes(`remote ${user} already exists`)) {
      throw error;
    }  
  }

  await logAndExec(`git fetch ${user}`);

  if (branch) {
    try {
      await logAndExec(`git checkout -b ${user}-${branch} ${user}/${branch}`);
    } catch (error) {
      if (error.message.includes(`branch named '${user}-${branch}' already exists`)) {
        await logAndExec(`git checkout ${user}-${branch}`);
      } else {
        throw error;
      }
    }

    await logAndExec(`git pull ${user} ${branch}`);
  }
}

main();