Why asynchronous code exists at all
JavaScript runs code line by line, in order. But some operations — like fetching data from a server — take time, and waiting for them to finish while freezing the entire page would be a bad experience for the user.
Asynchronous code lets you kick off a long-running operation, keep executing the rest of the code, and handle the result once it's ready — without the interface "freezing".
Promise — a promise of a future result
A Promise is an object representing the result of an operation that hasn't finished yet. It has three states: pending, fulfilled, and rejected. When the operation completes, the Promise "resolves" with a result or an error.
async/await — a friendlier syntax
async/await is a way to work with promises so the code reads like ordinary, sequential code instead of nested handler callbacks. A function is marked `async`, and `await` inside it "waits" for a result without blocking the rest of the page.
Frequently Asked Questions
When should I learn asynchronous JavaScript?
What's easier — Promise or async/await?
What's next
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