当表达式的值发生变化时，键块会销毁并重新创建其内容。如果你希望元素在值发生变化时播放其转换，而不是仅在元素进入或离开 DOM 时播放，则这很有用。
¥Key blocks destroy and recreate their contents when the value of an expression changes. This is useful if you want an element to play its transition whenever a value changes instead of only when the element enters or leaves the DOM.
例如，我们希望每当加载消息（即 i 发生变化）时，从 transition.js 播放 typewriter 转换。将 <p> 元素封装在一个关键块中：
¥Here, for example, we’d like to play the typewriter transition from transition.js whenever the loading message, i.e. i changes. Wrap the <p> element in a key block:
App
{#key i}
<p in:typewriter={{ speed: 10 }}>
{messages[i] || ''}
</p>
{/key}1
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<script>
import { typewriter } from './transition.js'; import { messages } from './loading-messages.js';let i = $state(-1);
$effect(() => { const interval = setInterval(() => {i += 1;
i %= messages.length;
}, 2500);
return () => {clearInterval(interval);
};
});
</script>
<h1>loading...</h1>
<p in:typewriter={{ speed: 10 }}> {messages[i] || ''}</p>