Svelte的强大核心是 响应式 的保持Dom和应用状态一致, 例如： 事件响应

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.

接下来是个计数器的例子。可以通过使用$state(...)把count变成响应式的。

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

let count = $state(0);

在Svelte中称这个$state为 rune (符文)，用来告诉Svelte count 可不是一个普通的变量。符文虽然看起来用起来都有点像函数，但是他们其实是语言的一部分。

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.

接下来需要做的就是实现 递增 了

All that’s left is to implement increment:

function increment() {
	count += 1;
}

$state rune是不是跟React的useState类似