watcher.js

const padEnd = require('string.prototype.padend');
const gaze = require('gaze');
const util = require('util');
const _ = require('lodash');
const chalk = require('chalk');
const { exec, spawn } = require('child_process');

const pexec = util.promisify(exec);
const log = (type, color = 'yellow') => (info, infoColor = 'reset') => {
  const tag = chalk[color](padEnd(type, 7));
  const sep = chalk.grey('|');
  const infoSerialized = chalk[infoColor](info.trim());
  process.stdout.write(`${tag}${sep} ${infoSerialized}\n\r`);
};

function build() {
  return pexec('yarn run build');
}

function createServer() {
  const server = spawn('yarn', ['start'], { env: process.env });
  const serverLog = log('server', 'blue');
  const serverErrorLog = log('error', 'red');
  server.stdout.on('data', data => serverLog(data.toString('utf8')));
  server.stderr.on('data', data =>
    serverErrorLog(data.toString('utf8'), 'red'));
  return server;
}

function killServer(child) {
  if (!child) return;
  child.stdin.pause();
  child.kill();
}

function recompile(config) {
  if (config.isCompiling) return;
  const { server } = config;
  const infoLog = log('info');
  Object.assign(config, { isCompiling: true });
  infoLog('Recompiling source', 'grey');
  build().then(() => {
    infoLog('Source recompiled', 'grey');
    infoLog('Restarting server', 'grey');
    killServer(server);
    const newServer = createServer();
    infoLog(`New server running ${newServer.pid}`, 'grey');
    Object.assign(config, {
      server: newServer,
      isCompiling: false,
    });
  });
}

const recompileDebounced = _.debounce(recompile, 500);

function startWatching() {
  const config = {};
  // initial compile
  recompile(config);
  gaze('src/**/*.js', function watch() {
    this.on('all', () => {
      recompileDebounced(config);
    });
  });
}

startWatching();