What is the Event Loop?

Event Loop — is a mechanism in JavaScript and other single-threaded environments that allows processing asynchronous operations without blocking the main thread.

Working principle:

• All synchronous operations are executed immediately and sequentially.
• Asynchronous operations (e.g., timers, network requests) are placed in the event queue.
• The Event Loop constantly checks the queue and, when the main thread is free, takes the next event from the queue and executes its associated callback.

This allows, for example, not to block the user interface while waiting for a server response.

Example:

console.log('Start');
setTimeout(() => {
  console.log('Asynchronous event');
}, 0);
console.log('End');

The output will be:

Start
End
Asynchronous event

Although the delay is 0, the callback will be executed after the synchronous code, thanks to the Event Loop.