SVELTE + VITE (二)

计算属性

<script>
	let count = 0;
	$: doubled = count * 2;

	function handleClick() {
		count += 1;
	}
</script>

<button on:click={handleClick}>
	Clicked {count} {count === 1 ? 'time' : 'times'}
</button>

<p>{count} doubled is {doubled}</p>

$: 类似于vue中的计算属性。通常指：组件状态的某些部分需要通过其它部分计算得出。

$:console.log(`the count is $count`)

$:{
    console.log(`the count is ${count}`)
    alert(`I SAID THE COUNT IS ${count}`)
}

$:if(count>=10){
    alert(`count is dangerously high!`);
    count = 9;
}

不仅可以声明反应式的值，通过可以运行反应式的语句，甚至可以将$:放在 if代码块前面

//app.svelte
<script>
	let count = 0;

	$: if (count >= 10) {
		alert(`count is dangerously high!`);
		count = 9;
	}

	function handleClick() {
		count += 1;
	}
</script>

<button on:click={handleClick}>
	Clicked {count} {count === 1 ? 'time' : 'times'}
</button>

组件属性传递

//子组件
//Nested.svelte

<script>
export let answer
</script>

<p>
    The answer is {answer}
</p>

//父组件
//App.svelte
<script>
import Nested from './Nested.svelte';
</script>

<Nested  answer={99} />

组件的props ,需要在子组件通过 export 关键字来做到。

//子组件 info.svelte
<script>
export let name;
export let version;
export let speed;
export let website;
</script>

<p>
	The <code>{name}</code> package is {speed} fast.
	Download version {version} from <a href="https://www.npmjs.com/package/{name}">npm</a>
	and <a href={website}>learn more here</a>
</p>

//父组件 App.svelte
<script>
	import Info from './Info.svelte';

	const pkg = {
		name: 'svelte',
		version: 3,
		speed: 'blazing',
		website: 'https://svelte.dev'
	};
</script>

<Info {...pkg}/>