Promises and the Fetch API

In a nutshell, a promise is an object that wraps asynchronous logic and provides methods to access the results or errors once operation completes. It is a proxy for the result value until it is known, and allows you to associate handler functions rather than using callbacks. It is a promise to supply the value once it is known and available.

To get a good feel for how promises are used, you will first be introduced to the Fetch API, which uses promises heavily. Then, we will backtrack and dive into a detailed description of the promises themselves.

Fetch is another API that enables you to make network requests and REST service calls, similar to jQuery's AJAX methods or the native XMLHttpRequest. The main difference is that the Fetch API uses promises, which has a cleaner and more concise syntax that helps you avoid callback hell.

Typical Fetch API usage for a JSON request looks something like this:

fetch(someURL)
    ...