Message Queue and Event Loop #607
Description
The Message Queue, also known as the Task Queue or Callback Queue, works in conjunction with the Event Loop to handle asynchronous operations in JavaScript. When asynchronous operations like setTimeout, HTTP requests, or DOM events complete, their callback functions are placed into the Message Queue. The Event Loop continuously monitors both the Call Stack and the Message Queue - when the Call Stack is empty, the Event Loop takes the first callback from the Message Queue and pushes it onto the Call Stack for execution. This mechanism ensures that JavaScript can handle asynchronous operations without blocking the main thread, allowing the browser to remain responsive to user interactions while waiting for time-consuming operations to complete. Additionally, ES6 introduced the concept of Microtasks (Promise callbacks and async/await operations), which have higher priority than regular tasks in the Message Queue and are processed immediately after the current script finishes executing but before any tasks from the Message Queue are handled.