Asynchronous JavaScript Overview

What is the initial state of a promise when it is created?

Which method can be used to handle successful outcomes of a promise?

What function is executed when a promise is resolved successfully?

What happens if you only pass one argument to the then() method?

Which method is specifically used for handling errors in promises?

What does the promise.then() call always return?

What is the role of chaining then() methods?

What is the purpose of the second function in the then() method?

What is a key characteristic of asynchronous execution in JavaScript?

Which of the following components are part of asynchronous JavaScript architecture?

What is a potential issue that arises from using callback functions?

What does the Promise() constructor require as its argument?

Which method is NOT mentioned as a way to handle asynchronous code?

Which function is called when a promise is resolved successfully?

What issue does callback hell primarily affect in a codebase?

What happens if an error occurs while executing a promise?

Asynchronous JavaScript

Asynchronous (or async) execution differs from the sequential order of code.
In asynchronous programming, the program doesn't halt while waiting for a task to finish; it proceeds to the next task.

Implementation Details

Asynchronous JavaScript utilizes a call stack, callback queue, Web APIs, and an event loop.
JavaScript engines comprise a memory heap (allocating memory) and a call stack (managing function calls).
Browsers contain Web APIs, an event loop, and a callback queue for asynchronous operations.

Asynchronous/Callback Functions

Different approaches exist (callbacks, promises, async/await) to handle asynchronous operations.
A callback is a function passed to another function, expected to run at a specific time.
The disadvantage of excessive use of callbacks is callback hell (nested structure).
Readability and maintainability decrease with complex nested callbacks.

Promises

A promise object is created using new Promise.
The Promise constructor accepts a function with two arguments: resolve (successful execution) and reject (error).
A promise begins in a pending state; it transitions to fulfilled if successful or rejected upon error.

Promise States

Promises can be in one of three states: pending (ongoing), fulfilled (successful), or rejected (failure).
When a server requests data using a promise, the initial state is pending; the fulfilled state occurs when retrieved successfully, and the rejected state indicates failure.

Promise Methods

then() is invoked after a promise resolves or rejects.
then() takes two functions: one for success and (optionally) one for error handling (catch()).

Promise Syntax

Promises can be used to pass a single argument for successful resolutions or have separate success cases and errors.

Additional Notes

.catch() is a method for handling errors.
.then() calls can be chained to handle one action after another, often utilizing values from previous actions.

This quiz explores the fundamentals of asynchronous JavaScript, focusing on its execution model, implementation details, and various handling methods such as callbacks, promises, and async/await. Understand the significance of the call stack, callback queue, and event loop in managing asynchronous tasks.