## What is a single-threaded language?

A **shingle-threaded** language is one that can execute only **one task at a time**. It executes the tasks one after the other, and each task has to finish before the next task starts. There is only one call stack, no parallel execution like in multhithreaded languages such as Java and C++

## How works the Call Stack in a single-threaded language?

The **Javascript call stack** works on a **"last in, first out"**. Only one function runs at a time. When a function finishes, it's removed of the stack. If something takes too long to finish, it blocks the stack, which means nothing else can run until it's done. For more information about how the call stack works, you can see my [post](http://localhost:3000/blog/article/call-stack-and-memory-heap) about the call stack.

## How can we prevent long running tasks from blocking our code?

There are several approaches to **prevent long-running tasks from blocking our code**. Some of these include using **asynchronous programming** techniques, such as Web API's callbacks, promises, async/await or **web workers**.

Web workers don't block our code because they run on a **separate thread** in the browser.

Asynchronous programming doesn't block our code because it uses the **event loop**,

## How does the event loop work?

1. The event loop starts by executing the code that is on the call stack. When it encounters asynchronous operations, it sends them to the Web Api, which is responsible to place them in the right queue. once the stack is empty (all synchronous tasks are completed), it checks the queues (callback queue, microtask queue )  to decide what will execute next. 
2.  Microtask queue has higher priority than the callback queue. The event loop will process all microtasks such as (promises resolutions, .then . catch) before moving to the callback queue.
4.  After microtask queue is emptied, the event loop will start procesing the calback queue (callbacks from web Api such as setTimeout, setInterval, event listeners)
5.  Will repeat this cycle over and over again

## Example:

```js
console.log('1: Start');

setTimeout(() => {
  console.log('2: setTimeout callback');
}, 0);

Promise.resolve().then(() => {
  console.log('3: Promise resolved');
});

console.log('4: End');

```

## The output will be:

1. Start
2. End
3. Promise resolved
4. setTimeout callback



The Single-Threaded Nature of Javascript

Understand how Javascript, being single-threaded, handles asynchronous operations using the call stack and event loop