JavaScript event loop is a mechanism that allows JavaScript code to run asynchronously. It works by waiting for events to happen, and then running the associated code when they do. This can be used to make sure that code doesn’t block the main thread, and to make sure that code runs in an order that makes sense.

The event loop has been around since the early days of JavaScript, but it was formalized in the HTML5 specification. The event loop is what makes things like animation and user input possible in JavaScript. When there is nothing else for the event loop to do, it will “sleep” until an event happens. When an event happens, the associated code will run, and then the event loop will go back to sleep.

There are a few different types of events that can happen:

  • Timer events: These happen after a certain amount of time has passed (e.g., setTimeout() ).
  • User input events: These happen when the user interacts with the page (e.g., click ).
  • Network events: These happen when data is received from a network request (e.g., XMLHttpRequest ).
  • DOM events: These happen when something changes in the DOM (e.g., document ready).

Each of these types of events has its own queue. When an event happens, it is added to its respective queue. The event loop will then process each queue one at a time.

For timer events, this means that the callback function will be called after the specified time has elapsed. For user input events, this means that the callback function will be called when the user interacts with the element on which the event listener is registered. For network events, this means that the callback function will be called when data is received from the network request. And for DOM events, this means that the callback function will be called when something changes in the DOM.

In addition to these four queues, there is also a microtask queue. This queue is processed after each of the other queues has been processed. Microtasks are used for tasks such as Promises and process .nextTick().

The event loop will continue to run until there are no more tasks left to do . Once all of the queues have been processed, if there are no more tasks left to do, then the event loop will go back to sleep until another event happens . Docker is a tool that enables you to create, deploy, and run applications by using containers. Containers allow you to package up an application with all of the parts it needs, such as libraries and other dependencies, and ship it all out as one package. By doing this, you can control exactly what your application runs on, regardless of the environment.

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