Event loop overview in Javascript - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the event loop in JavaScript?

The event loop is a process that allows JavaScript to perform non-blocking operations by handling asynchronous callbacks and managing the execution of code, events, and tasks in a single thread.

beginner

What are the main parts involved in the event loop?

The main parts are the call stack, the callback queue (or task queue), and the event loop itself which moves tasks from the queue to the stack when the stack is empty.

beginner

How does the call stack work in the event loop?

The call stack keeps track of function calls. When a function is called, it is added to the stack. When it finishes, it is removed. The event loop waits for the stack to be empty before processing new tasks.

beginner

What happens when an asynchronous operation completes in JavaScript?

When an async operation finishes, its callback is placed in the callback queue. The event loop then waits for the call stack to be empty before moving the callback to the stack to run.

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Why is the event loop important for JavaScript?

Because JavaScript runs in a single thread, the event loop allows it to handle multiple tasks without freezing the program, making it responsive and efficient.

What does the event loop do in JavaScript?

A Stores variables and functions

B Runs multiple threads simultaneously

C Manages asynchronous callbacks and keeps the program responsive

D Compiles JavaScript code to machine code

The event loop manages asynchronous callbacks and ensures JavaScript stays responsive by handling tasks in a single thread.

Where are completed asynchronous callbacks placed before execution?

A Call stack

B Heap memory

C Global scope

D Callback queue

Completed asynchronous callbacks go to the callback queue, waiting for the call stack to be empty.

When does the event loop move a callback from the queue to the call stack?

A When the call stack is empty

B Immediately after the callback is created

C When the browser refreshes

D When the user clicks a button

The event loop moves callbacks to the call stack only when the stack is empty to avoid blocking.

Which of these is NOT part of the event loop mechanism?

A Database server

B Call stack

C Event loop

D Callback queue

The database server is external and not part of the event loop mechanism.

Why does JavaScript use an event loop?

A To run code faster by using multiple threads

B To handle asynchronous tasks without blocking the main thread

C To compile code before running

D To store user data

JavaScript uses the event loop to handle asynchronous tasks efficiently in a single thread.

Explain how the event loop manages asynchronous tasks in JavaScript.

Think about how JavaScript keeps running smoothly even with delays.

Describe the roles of the call stack and callback queue in the event loop.

Imagine a line of tasks waiting to be done one by one.