Callback Queue VS Microtask Queue 

In this lecture, you will learn what is Callback queue and Microtask Queue and which one takes the priority over another.
A callback function can wait for its execution in any one of the queue i.e. callback queue or microtask queue and once the call stack is empty, event loop pushes the callback functions from these queues to call stack for there execution.
Microtask queue takes priority over the callback queue and callback functions of Microtask queue are executed first. Once all the functions of callback queue are executed completely, then only callback functions of callback queue gets executed.