Node.js, the single-threaded champion of the JavaScript world! Well, maybe not champion, but at least somewhat famous for being single-threaded. But wait! Does this mean that concurrency in Node.js is a myth and we shouldn't even think about it? Let's explore this together and see what the story is!

Node.js: The Lovable Single-Thread!

First of all, we must accept that Node.js is indeed single-threaded. What does that mean? It means it only has one line to get things done. Imagine you have a restaurant with a very fast and professional waiter, but only one waiter! They have to take orders, prepare food, and do the bookkeeping. Well, naturally, things might slow down in some places, right?

The exact same thing happens in Node.js. If we give it a very heavy task (like processing a large file or complex calculations), it might completely freeze and no longer respond to other requests. This state is called "Blocking". Not pleasant at all, is it?

So what's the solution? Everything Changes with Async/Await!

This is where async/await comes to our rescue! These two magical words help us perform our tasks asynchronously. What does that mean? It means our waiter (Node.js) can give an order to the kitchen (a heavy operation), then go take another order, and when the food is ready (the operation is complete), come back and deliver the food.

In other words, async/await allows Node.js to respond to other requests while waiting for a heavy operation. This way there's no more freezing and everything goes much faster and smoother.

Practical Example of Async/Await:

Suppose we want to read a file:

async function readFileAsync(filePath) {
  try {
    const data = await fs.promises.readFile(filePath, 'utf8');
    console.log(data);
  } catch (error) {
    console.error('Error reading file:', error);
  }
}

readFileAsync('myfile.txt');

In this example, the readFileAsync function uses await to wait for the file to be read. Meanwhile, Node.js can respond to other requests.

Forget Callback Hell!

Before async/await, programmers had to use Callback functions. Callbacks get the job done, but when there are too many of them, the code becomes very complex and incomprehensible. This state is called "Callback Hell". Fortunately, async/await helps us escape this nightmare and write cleaner, more readable code.

Multi-threading: When One Waiter Isn't Enough!

With all that, there are times when async/await doesn't work either. For example, when we are doing a series of very heavy calculations that occupy the CPU to the max. This is where we should think about multi-threading.

What is multi-threading? It means hiring several waiters! In Node.js we can use modules like worker_threads to create multiple threads and divide our tasks between them. This way the CPU doesn't get tired and everything is done much faster.

Important note about multi-threading:

Using multi-threading in Node.js is a bit complex and requires accuracy. We must be careful that the threads do not interfere with each other and that data is transferred correctly between them.

Node.js Concurrency: Conclusion

So, is concurrency impossible in Node.js? No! Despite being single-threaded, Node.js provides us with powerful tools like async/await and worker_threads to perform our tasks concurrently and optimally. We just need to know when and where to use which tool.

In Summary:

Node.js is single-threaded.
async/await helps us perform our tasks asynchronously.
Multi-threading is suitable for very heavy and CPU-bound tasks.

I hope this article has been helpful to you. If you have any questions, be sure to ask!