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JavaScript Asynchronous Programming with JavaScript Understanding Promises Perform Cleanup With finally()

Posted by jun cheng wong
jun cheng wong
17,021 Points

How promises perform asynchronous tasks?

I understand how callback works asynchronously, but I cannot understand how promise does it.

Reggie Williams
Reggie Williams
Treehouse Teacher
Reggie Williams
Reggie Williams
Treehouse Teacher

Hey jun cheng wong promises work like callbacks and differ in syntax. Which part of promises were you unsure about?

jun cheng wong
jun cheng wong
17,021 Points

Hi, can you provide me an example of how promises not blocking the other code to run?

1 Answer

JASON LEE
JASON LEE
17,352 Points
JASON LEE
JASON LEE
17,352 Points

If you understand how callback works asynchronously, then you can see when declaring a new Promise, it accepts a parameter which is a callback function. Promise uses a callback function, and callback function works asynchronously, therefore Promise works asynchronously.

The callback function is the one that is passed two arguments (resolve and reject).

This is my understanding so someone feel free to correct me if I'm wrong.

EDIT: I am not sure whether or not callback functions by themselves are asynchronous (probably not?), but they are often seen in asynchronous operations due to the ordering in which it's executed. Also now I'm second guessing whether I used the proper terms: parameter vs argument, or vice-versa. Because if you can't distinguish parameter vs argument, esp. when working with callback/higher order functions, it's really easy to get lost. Someone please advise.