Macro-tasks within an event loop (Summary)

Macro-tasks within an event loop: Macro-task represents some discrete and independent work. These are always the execution of thee JavaScript code and micro-task queue is empty. Macro-task queue is often considered the same as the task queue or the event queue. However, the macro-task queue works the same as the task queue. The only small difference between the two is that the task queue is used for synchronous statements whereas the macro-task queue is used for asynchronous statements.

In JavaScript, no code is allowed to execute until an event has occurred. {It is worth mentioning that the execution of a JavaScript code execution is itself a macro-task.} The event is queued as a macro-task. When a (macro) task, present in the macro-task queue is being executed, new events may be registered and in turn created and added to the queue.

Up on initialization, the JavaScript engine first pulls off the first task in the macro-task queue and executes the callback handler. The JavaScript engine then sends these asynchronous functions to the API module, and the module pushes them to the macro-task queue at the right time. Once inside the macro-task queue, each macro-task is required to wait for next round of event loop. In this way, the code is executed.

All micro-tasks logged are processed in one fell swoop in a single macro-task execution cycle. In comparison, the macro-task queue has a lower priority. Macro-tasks include parsing HTML, generating DOM, executing main thread JavaScript code and other events such as page loading, input, network events, timer events, etc.

Examples: setTimeout, setInterval, setImmediate, requestAnimationFrame, I/O, UI Rendering