`worker_thread` example

node-handlebars-worker.js

/**
 * @file  This creates a worker thread that only handles template rendering.
 *        The purpose is to keep the main thread free so that processes like
 *        rendering don't block the event loop.
 */

const {
  Worker, isMainThread, parentPort
} = require('worker_threads');

if (isMainThread) {
  const worker = new Worker(__filename);

  exports.render = function(template, data) {
    return new Promise((resolve, reject) => {
      const id = Date.now() + Math.random();

      worker.postMessage({ id, template, data });

      function onmessage(response) {
        if (response.id === id) {
          if (response.error) {
            reject(response.error);
          } else {
            resolve(response.data);
          }
          worker.off('message', onmessage);
        }
      }

      worker.on('message', onmessage);

      setTimeout(function() {
        reject(new Error('Timeout exceeded. Try again in a few seconds.'));
        worker.off('message', onmessage);
      }, 15000);
    });
  };
} else {
  const Handlebars = require('handlebars');

  parentPort.on('message', function(request) {
    try {
      const data = Handlebars.compile(request.template)(request.data);
      parentPort.postMessage({ id: request.id, data });
    } catch (error) {
      parentPort.postMessage({ id: request.id, error });
    }
  });
}