Bare-bones nodemon + esbuild hybrid for hot-reloading a process

develop.js

//@ts-check
'use strict';

const ChildProcess = require('child_process');
const Events = require('events');
const Path = require('path');

const { watch } = require('chokidar');
const { startService } = require('esbuild');
const Pino = require('pino');

async function buildApi(logger) {
  process.chdir(__dirname);

  const service = await startService();
  const watcher = watch(Path.resolve(__dirname, './src/**/*'), {
    interval: 20,
  });
  const start = Date.now();
  const build = await service.build({
    bundle: true,
    define: {
      'process.env.NODE_ENV': JSON.stringify(process.env.NODE_ENV || 'development'),
    },
    format: 'cjs',
    incremental: true,
    mainFields: ['module', 'main'],
    platform: 'node',
    write: true,
    target: 'node10',
    entryPoints: ['./src/index.ts'],
    outdir: './dist',
  });

  logger.info({ latency: Date.now() - start, warnings: build.warnings }, 'initial build complete');

  const rebuild = async () => {
    const start = Date.now();

    try {
      const rebuild = await build.rebuild();

      logger.info({ latency: Date.now() - start, warnings: rebuild.warnings }, 'rebuild complete');

      await postBuild();
    } catch (err) {
      logger.error({ err }, 'error while attempting to rebuild');
    }
  };

  const postBuild = async () => {
    if (child && !Number.isInteger(child.exitCode)) {
      logger.info({ childPid: child.pid }, 'sending SIGKILL to managed process');

      child.kill('SIGTERM');

      const [exitCode] = await Events.once(child, 'exit');

      logger.info({ exitCode, childPid: child.pid }, 'managed process exited');
    }

    child = ChildProcess.spawn('node', [Path.join(__dirname, 'dist/index.js')], {
      stdio: ['ignore', 'inherit', 'inherit'],
    });

    logger.info({ childPid: child.pid }, 'managed process spawned');
  };

  /** @type {import('child_process').ChildProcess | undefined} */
  let child = undefined;

  let queue = postBuild();

  watcher.on('all', (e) => {
    queue = queue.then(rebuild);
  });
}

async function main(logger) {
  await buildApi(logger);
}

const logger = Pino({
  prettyPrint: process.env.NODE_ENV !== 'production',
});

main(logger).catch((err) => {
  logger.fatal({ err }, 'uncaught exception');
  process.exit(1);
});