feat: apply inert to outroing elements (#8628)

that way they are invisible to assistive technology and can't be interacted with, which makes sense since the element is already "dead" and only transitioning out at this point
closes #8445

Author: dummdidumm

CHANGELOG.md

@@ -16,6 +16,7 @@
 * **breaking** Error on falsy values instead of stores passed to `derived` ([#7947](https://github.com/sveltejs/svelte/pull/7947))
 * **breaking** Custom store implementers now need to pass an `update` function additionally to the `set` function ([#6750](https://github.com/sveltejs/svelte/pull/6750))
 * **breaking** Change order in which preprocessors are applied ([#8618](https://github.com/sveltejs/svelte/pull/8618))
+* **breaking** apply `inert` to outroing elements ([#8627](https://github.com/sveltejs/svelte/pull/8627))
 * Add a way to modify attributes for script/style preprocessors ([#8618](https://github.com/sveltejs/svelte/pull/8618))
 * Improve hydration speed by adding `data-svelte-h` attribute to detect unchanged HTML elements ([#7426](https://github.com/sveltejs/svelte/pull/7426))
 * Add `a11y no-noninteractive-element-interactions` rule ([#8391](https://github.com/sveltejs/svelte/pull/8391))

src/runtime/internal/transitions.js

@@ -186,14 +186,15 @@ export function create_in_transition(node, fn, params) {
  * @returns {{ end(reset: any): void; }}
  */
 export function create_out_transition(node, fn, params) {
-	/**
-	 * @type {TransitionOptions} */
+	/** @type {TransitionOptions} */
 	const options = { direction: 'out' };
 	let config = fn(node, params, options);
 	let running = true;
 	let animation_name;
 	const group = outros;
 	group.r += 1;
+	/** @type {boolean} */
+	let original_inert_value;
 
 	/**
 	 * @returns {void} */
@@ -205,10 +206,18 @@ export function create_out_transition(node, fn, params) {
 			tick = noop,
 			css
 		} = config || null_transition;
+
 		if (css) animation_name = create_rule(node, 1, 0, duration, delay, easing, css);
+
 		const start_time = now() + delay;
 		const end_time = start_time + duration;
 		add_render_callback(() => dispatch(node, false, 'start'));
+
+		if ('inert' in node) {
+			original_inert_value = /** @type {HTMLElement} */ (node).inert;
+			node.inert = true;
+		}
+
 		loop((now) => {
 			if (running) {
 				if (now >= end_time) {
@@ -229,6 +238,7 @@ export function create_out_transition(node, fn, params) {
 			return running;
 		});
 	}
+
 	if (is_function(config)) {
 		wait().then(() => {
 			// @ts-ignore
@@ -238,8 +248,12 @@ export function create_out_transition(node, fn, params) {
 	} else {
 		go();
 	}
+
 	return {
 		end(reset) {
+			if (reset && 'inert' in node) {
+				node.inert = original_inert_value;
+			}
 			if (reset && config.tick) {
 				config.tick(1, 0);
 			}
@@ -274,6 +288,9 @@ export function create_bidirectional_transition(node, fn, params, intro) {
 	let pending_program = null;
 	let animation_name = null;
 
+	/** @type {boolean} */
+	let original_inert_value;
+
 	/**
 	 * @returns {void} */
 	function clear_animation() {
@@ -318,11 +335,25 @@ export function create_bidirectional_transition(node, fn, params, intro) {
 			start: now() + delay,
 			b
 		};
+
 		if (!b) {
 			// @ts-ignore todo: improve typings
 			program.group = outros;
 			outros.r += 1;
 		}
+
+		if ('inert' in node) {
+			if (b) {
+				if (original_inert_value !== undefined) {
+					// aborted/reversed outro — restore previous inert value
+					node.inert = original_inert_value;
+				}
+			} else {
+				original_inert_value = /** @type {HTMLElement} */ (node).inert;
+				node.inert = true;
+			}
+		}
+
 		if (running_program || pending_program) {
 			pending_program = program;
 		} else {

test/runtime/samples/transition-inert/_config.js

@@ -0,0 +1,28 @@
+export default {
+	async test({ assert, component, target, raf }) {
+		// jsdom doesn't set the inert attribute, and the transition checks if it exists, so set it manually to trigger the inert logic
+		target.querySelector('button.a').inert = false;
+		target.querySelector('button.b').inert = false;
+
+		// check and abort halfway through the outro transition
+		component.visible = false;
+		raf.tick(50);
+		assert.strictEqual(target.querySelector('button.a').inert, true);
+		assert.strictEqual(target.querySelector('button.b').inert, true);
+
+		component.visible = true;
+		assert.strictEqual(target.querySelector('button.a').inert, false);
+		assert.strictEqual(target.querySelector('button.b').inert, false);
+
+		// let it transition out completely and then back in
+		component.visible = false;
+		raf.tick(101);
+		component.visible = true;
+		raf.tick(50);
+		assert.strictEqual(target.querySelector('button.a').inert, false);
+		assert.strictEqual(target.querySelector('button.b').inert, false);
+		raf.tick(51);
+		assert.strictEqual(target.querySelector('button.a').inert, false);
+		assert.strictEqual(target.querySelector('button.b').inert, false);
+	}
+};

test/runtime/samples/transition-inert/main.svelte

@@ -0,0 +1,16 @@
+<script>
+	export let visible = true;
+
+	function slide(_, params) {
+		return params;
+	}
+</script>
+
+{#if visible}
+	<button class="a" transition:slide={{ duration: 100 }}>
+		foo
+	</button>
+	<button class="b" out:slide={{ duration: 100 }}>
+		bar
+	</button>
+{/if}