ASYNC / AWAIT /// PROMISES /// EVENT LOOP /// THEN CATCH /// ASYNC / AWAIT /// PROMISES /// EVENT LOOP /// THEN CATCH /// ASYNC / AWAIT /// PROMISES ///

JS Promises

Master the flow of time in JavaScript. Say goodbye to Callback Hell and hello to clean Async/Await architectures.

promises.js
1 / 13
12345

A.D.A:JavaScript is single-threaded. This means it can only execute one task at a time. But what happens if a task takes a long time, like fetching data from an API? We don't want the browser to freeze.


Async Matrix

UNLOCK NODES BY MASTERING ASYNC CONCEPTS.

Concept: Promises

Promises manage asynchronous operations, moving from Pending to Fulfilled or Rejected.

System Check

Which constructor is used to create a new Promise?

Community Holo-Net

Showcase Your Architecture

ACTIVE

Built an impressive async flow? Share your JS Promise patterns.

JavaScript Promises

Author

Pascual Vila

Senior Developer // Code Syllabus

JavaScript is single-threaded. To prevent long-running tasks from freezing the browser, we use Asynchronous Programming. Promises are the modern foundation of async JS.

What is a Promise?

A Promise is an object representing the eventual completion or failure of an asynchronous operation. Think of it like a restaurant buzzer: you place an order, they give you a buzzer (the Promise). You can keep chatting with your friends (synchronous code keeps running), and eventually, the buzzer rings (the Promise resolves).

Then and Catch

Once a Promise is created, you need to handle its outcome. We use the.then() method to schedule a callback for when the Promise is fulfilled. For errors, we chain a.catch() method. This prevents the "Callback Hell" (Pyramid of Doom) common in older JS code.

Async / Await

Introduced in ES2017, async/await provides a more readable, synchronous-looking syntax for working with Promises. By placing async before a function, it automatically returns a Promise. Inside it, await pauses the function execution until the Promise settles.

Async Glossary

Promise

An object representing the eventual completion (or failure) of an asynchronous operation.

Pending

The initial state of a Promise. Neither fulfilled nor rejected.

Fulfilled

The state of a Promise representing a successful operation. Triggered by resolve().

Rejected

The state of a Promise representing a failed operation. Triggered by reject().

.then()

A method that returns a Promise. It takes up to two arguments: callback functions for the success and failure cases.

.catch()

A method used to handle rejected Promises in a chain.

async

Keyword used to declare an asynchronous function. It ensures that the function returns a promise.

await

Keyword that pauses the execution of an async function until a Promise settles.

Support Us