At the heart of Svelte is a powerful system of reactivity for keeping the DOM in sync with your application state — for example, in response to an event.

Make the count declaration reactive by wrapping the value with $state(...):

let count = $state(0);

This is called a rune, and it’s how you tell Svelte that count isn’t an ordinary variable. Runes look like functions, but they’re not — when you use Svelte, they’re part of the language itself.

All that’s left is to implement increment:

function increment() {
	count += 1;
}