Quick JavaScript Crash Course - Modern and Advanced JavaScript - Promises-all Settled-vs-all

The lecture introduces promises in JavaScript, focusing on the Promise.allSettled method introduced in ES2020. It explains how promises work, including creating, resolving, and rejecting them. The lecture also compares Promise.allSettled with Promise.all, highlighting their differences in handling multiple promises. Practical examples demonstrate how these methods manage asynchronous operations, emphasizing the importance of handling both resolved and rejected states.

What is the primary purpose of using promises in JavaScript?

• To create loops

• To handle synchronous operations

• To define variables

• To manage asynchronous operations

Which method is used to handle errors in a promise chain?

• catch

• then

• finally

• resolve

What happens when a promise is rejected?

• It goes to the catch block

• It stops execution

• It continues to the next then block

• It restarts the promise

Why might you use Promise.allSettled over Promise.all?

• To handle only the first rejected promise

• To get results of all promises regardless of their state

• To handle only the first resolved promise

• To ignore all promises

What is the key difference between Promise.all and Promise.allSettled?

• Promise.all is only for synchronous operations

• Promise.allSettled is faster than Promise.all

• Promise.allSettled stops at the first rejection, while Promise.all waits for all to settle

• Promise.allSettled waits for all promises to settle, while Promise.all stops at the first rejection

In the context of promises, what does 'settled' mean?

• A promise is still pending

• A promise is either resolved or rejected

• A promise is only rejected

• A promise is only resolved

What does Promise.all return if one of the promises is rejected?

• The first resolved value

• The rejected value

• An error message

• An array of resolved values

How does Promise.allSettled handle rejected promises?

• It retries them

• It stops execution

• It includes them in the results with a status of 'rejected'

• It ignores them

What is a practical use case for Promise.allSettled?

• When you need the result of the first resolved promise

• When you want to execute promises sequentially

• When you want to handle all promises regardless of their outcome

• When you only care about rejected promises

Which ES version introduced Promise.allSettled?

• ES2015

• ES2017

• ES2020

• ES2021