Let’s Talk About Promises in JavaScript!!!

In today’s post, I’m going back to Vanilla JavaScript and we’re talking about the Promise Object!! These are used when handling asynchronous actions so without a doubt, you will run into them at some point! A common use case is when dealing with API’s and you have to wait for the request to be processed.

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What is a Promise?

A promise is a JavaScript object containing ‘Producing Code’ and ‘Consuming Code’.

Producing Code — Code that takes time.

Consuming Code — Code that must wait for a result.

JS Promises operate similarly to real life ones. Initially they’re pending and then they are either fulfilled (success) or rejected (not been kept, there’s an error!).

Promises have 2 properties: ‘State’ and ‘Result’.

The result is either undefined, a result value or an error object.

See the diagram for more details!!

Methods:

.then() follows a successful promise, usually an additional step!

For e.g., check out the pseudocode below:

fetch(“API_ENDPOINT”).then(response => response.json).then(data => console.log(data))

.catch() catches errors.

Examples:

Waiting for a timeout.

Waiting for a file.

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