What is the precise behavior of the Event Loop when a Promise microtask is queued during the execution of a synchronous task?

Question

Web Development — Hard

What is the precise behavior of the Event Loop when a Promise microtask is queued during the execution of a synchronous task?

Accepted Answer

The Event Loop processes the call stack until empty. Once the stack is empty, it processes all tasks in the microtask queue (Promises, MutationObserver) before moving to the next macrotask or rendering phase. Option A is incorrect because it ignores the requirement for the call stack to be empty. Option B is incorrect as microtasks have higher priority than macrotasks. Option D is incorrect because JavaScript is single-threaded.