This tutorial from Josh Comeau provides an in-depth look at Promises in JavaScript, which were designed to solve the 'callback hell' problem with asynchronous code.

Key points:

• JavaScript is single-threaded and can't block the main thread, leading to the need for asynchronous code

• Callbacks were the original way to handle asynchronous operations, but led to callback hell

• Promises represent the eventual success or failure of an async operation

• .then() is used to chain Promises and pass data to the next step

• .catch() handles Promise rejections when an error occurs

• async/await syntax allows writing async code in a synchronous style, powered by Promises under the hood