高级反应性 / 原始状态 • Svelte Tutorial

高级 Svelte 高级反应性原始状态

在之前的练习中，我们了解到状态是深度响应 — 如果你（例如）更改对象的属性或推送到数组，它将导致 UI 更新。这通过创建一个拦截读取和写入的 proxy 来实现。

¥In previous exercises, we learned that state is deeply reactive — if you (for example) change a property of an object, or push to an array, it will cause the UI to update. This works by creating a proxy that intercepts reads and writes.

有时，这不是你想要的。如果你不更改单个属性，或者保持引用相等很重要，那么你可以改用原始状态。

¥Occasionally, that’s not what you want. If you’re not changing individual properties, or if it’s important to maintain referential equality, then you can use raw state instead.

在此示例中，我们有一张 Svelte 稳步上涨的股价图表。我们希望图表在有新数据时更新，我们可以通过将 data 转换为状态来实现...

¥In this example, we have a chart of Svelte’s steadily increasing stock price. We want the chart to update when new data comes in, which we could achieve by turning data into state...

App

let data = $state(poll());

...但当它在几毫秒后被丢弃时，没有必要让它具有深度响应性。改为使用 $state.raw：

¥...but there’s no need to make it deeply reactive when it will be discarded a few milliseconds later. Instead, use $state.raw:

App

let data = $state.raw(poll());

改变原始状态不会产生直接影响。一般来说，强烈不建议改变非反应状态。

¥[!NOTE] Mutating raw state will have no direct effect. In general, mutating non-reactive state is strongly discouraged.

关键块反应式类

<script>

	import { scale } from './utils.js';

	import { poll } from './data.js';

	let data = poll();

	let w = $state(1);

	let h = $state(1);

	const min = $derived(Math.min(...data) - 5);

	const max = $derived(Math.max(...data) + 5);

	const x = $derived(scale([0, data.length], [0, w]));

	const y = $derived(scale([min, max], [h, 0]));

	const ticks = $derived.by(() => {

		const result = [];

		let n = 10 * Math.ceil(min / 10);

		while (n < max) {

			result.push(n);

			n += 10;

		return result;

});

	$effect(() => {

		const interval = setInterval(() => {

			data = poll();

		}, 200);

		return () => {

			clearInterval(interval);

};

});

</script>

<div class="outer">

	<svg width={w} height={h} bind:clientWidth={w} bind:clientHeight={h}>

		<line y1={h} y2={h} x2={w} />

		{#each ticks as tick}

			<g class="tick" transform="translate(0,{y(tick)})">

				<line x2={w} />

				<text x={-5}>{tick}</text>

			</g>

		{/each}

		<polyline points={data.map((d, i) => [x(i), y(d)]).join(' ')} />

		<text x={10} y={10} font-size={36}>$SVLT</text>

	</svg>

</div>

<style>

	.outer {

		width: 100%;

		height: 100%;

		padding: 2em;

		box-sizing: border-box;

	svg {

		width: 100%;

		height: 100%;

		overflow: visible;

	polyline {

		fill: none;

		stroke: #ff3e00;

		stroke-width: 2;

		stroke-linejoin: round;

		stroke-linecap: round;

	line {

		stroke: #aaa;

	.tick {

		stroke-dasharray: 2 2;

		text {

			text-anchor: end;

			dominant-baseline: middle;

</style>

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