Intro to multithreaded JavaScript | InfoWorld

Server-side threading with worker threads

Now let’s take a look at the server side, using Node.js. In this case, instead of web workers, we use the concept of a worker thread. A worker thread is similar to a web worker in that we pass messages back and forth from the main thread to the worker. 

For example, let’s say we have two files, main.js and worker.js. We’ll run main.js (using the command: node main.js) and it will spawn a thread by loading worker.js as a worker thread. Here is our main.js file:

const { Worker } = require('worker_threads');

function fetchPersonWithWorker(id) {
  return new Promise((resolve, reject) => {
    const worker = new Worker('./worker.js', { workerData: id });

    worker.on('message', (data) => {
      if (data.error) {
        reject(data.error);
      } else {
        resolve(data);
      }
      worker.terminate();
    });

    worker.on('error', (error) => reject(error));

    let url = `https://swapi.dev/api/people/${id}`;
    worker.postMessage({ url });
  });
}

const lukeId = 1;
const leiaId = 5;

console.log("Fetching Star Wars characters with worker threads...");

Promise.all([fetchPersonWithWorker(lukeId), fetchPersonWithWorker(leiaId)])
  .then(data => {
    console.log("Characters received: "+ JSON.stringify(data) );
    console.log(data[0]); // Data for Luke Skywalker (ID: 1)
    console.log(data[1]); // Data for Leia Organa (ID: 5)
  })
  .catch(error => console.error("Error fetching characters:", error));

console.log("Moving on to other things...");

We import Worker from the worker_threads module, but note that it’s built into Node, so we don’t need NPM for this. To launch the worker, we create a new Worker object and give it the worker.js file as a parameter. Once that is done, we add a message listener that resolves or rejects our promise—this is exactly like we did for the web worker. We also terminate the worker when done, to clean up the resources.