What is the Event Loop?
Phases of the Event Loop
- Call Stack:
- The call stack is where synchronous code is executed.
- Functions are pushed onto the stack and popped off when they complete.
- Callback Queue:
- Asynchronous operations, such as API calls or user interactions, are processed in the callback queue.
- Callbacks from these operations are queued up to be executed once the call stack is empty.
- Event Loop:
- The event loop constantly checks if the call stack is empty.
- If the stack is empty, it moves callbacks from the queue to the stack for execution.
- Microtask Queue:
- Microtasks are high-priority tasks that are executed before the next event loop cycle.
- Promises and certain APIs schedule tasks in the microtask queue.
How the Event Loop Handles Asynchronous Operations
Let’s take a look at how the event loop manages asynchronous tasks:
- setTimeout allows you to schedule a function to run after a specified delay.
- The specified function is added to the callback queue after the delay.
- Promises are a powerful tool for handling asynchronous operations.
- They use the microtask queue, ensuring their callbacks are executed before the next event loop cycle.
- Async/Await, built on top of Promises, provides a more readable way to work with asynchronous code.
- Under the hood, it still relies on the event loop and the microtask queue.