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fix: reset title element to previous value on removal #14116

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c9f5147
fix: reset title element to previous value on removal
dummdidumm Nov 2, 2024
3265021
export $.title
Rich-Harris Nov 4, 2024
963d393
Merge branch 'main' into title-removal-fix
Rich-Harris Dec 4, 2024
2072638
fixes
Rich-Harris Dec 4, 2024
3904b8f
belt and braces
Rich-Harris Dec 4, 2024
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2 changes: 1 addition & 1 deletion packages/svelte/src/compiler/phases/3-transform/client/visitors/TitleElement.js
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Original file line number Diff line number Diff line change
Expand Up @@ -14,7 +14,7 @@ export function TitleElement(node, context) {
context.state
);

const statement = b.stmt(b.assignment('=', b.id('$.document.title'), value));
const statement = b.stmt(b.call('$.title', value));

if (has_state) {
context.state.update.push(statement);
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15 changes: 15 additions & 0 deletions packages/svelte/src/internal/client/dom/elements/misc.js
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Original file line number Diff line number Diff line change
@@ -1,3 +1,4 @@
import { render_effect } from '../../reactivity/effects.js';
import { hydrating } from '../hydration.js';
import { clear_text_content, get_first_child } from '../operations.js';
import { queue_micro_task } from '../task.js';
Expand Down Expand Up @@ -56,3 +57,17 @@ export function add_form_reset_listener() {
);
}
}

/**
* @param {string} text
*/
export function title(text) {
render_effect(() => {
const previous = document.title;
document.title = text;

return () => {
document.title = previous;
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@dummdidumm dummdidumm Dec 6, 2024 •
edited
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This should handle another edge case - thoughts?

Suggested change
document.title = previous;
// Preserve later updates to title from other sources
if (document.title === text) {
document.title = previous;
}

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Which case would this prevent? It actually seems to me like this might make bugs more likely, since if a component had a <title> and also contained a component that set document.title in a user effect, it wouldn't revert either when the parent was removed

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This handles the case where A sets the title, then B is mounted and sets the title, then A updates the title (in other words it contains something like <title>{foo}</title>), then B is removed - in that case we wouldn't want the title to be reverted back to what A had initially, we want to preserve the title.

Setting document.title in a user effect manually feels a bit like "working against the framework", you should just do that declaratively.

They are both edge cases either way, so I'm ok with not adding this suggestion.

Comment on lines +66 to +70
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@dummdidumm dummdidumm Dec 10, 2024 •
edited
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We can also do this, would handle the case described in https://github.com/sveltejs/svelte/pull/14116/files#r1876874053

Suggested change
const previous = document.title;
document.title = text;
return () => {
document.title = previous;
const previous = document.title;
const own = {};
// @ts-expect-error
document._last_title_setter = own;
document.title = text;
return () => {
// @ts-expect-error
if (document._last_title_setter === own) {
document.title = previous;
}

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Looking at how the code is generated, we should switch it up anyway - right now if your title would contain dynamic content, you would set it two times on an update - once to revert to the previous value, then right away again for the updated value. Wasteful.

};
});
}
2 changes: 1 addition & 1 deletion packages/svelte/src/internal/client/index.js
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Expand Up @@ -38,7 +38,7 @@ export {
} from './dom/elements/attributes.js';
export { set_class, set_svg_class, set_mathml_class, toggle_class } from './dom/elements/class.js';
export { apply, event, delegate, replay_events } from './dom/elements/events.js';
export { autofocus, remove_textarea_child } from './dom/elements/misc.js';
export { autofocus, remove_textarea_child, title } from './dom/elements/misc.js';
export { set_style } from './dom/elements/style.js';
export { animation, transition } from './dom/elements/transitions.js';
export { bind_active_element } from './dom/elements/bindings/document.js';
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4 changes: 2 additions & 2 deletions packages/svelte/tests/runtime-runes/samples/if-dependency-order-2/_config.js
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Expand Up @@ -5,7 +5,7 @@ export default test({
async test({ assert, target, window }) {
const [btn1] = target.querySelectorAll('button');

assert.htmlEqual(window.document.head.innerHTML, ``);
assert.htmlEqual(window.document.head.innerHTML, `<title>initial</title>`);

flushSync(() => {
btn1.click();
Expand All @@ -17,6 +17,6 @@ export default test({
btn1.click();
});

assert.htmlEqual(window.document.head.innerHTML, `<title>hello world</title>`);
assert.htmlEqual(window.document.head.innerHTML, `<title>initial</title>`);
}
});
4 changes: 4 additions & 0 deletions packages/svelte/tests/runtime-runes/samples/if-dependency-order-2/main.svelte
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Expand Up @@ -8,6 +8,10 @@
}
</script>

<svelte:head>
<title>initial</title>
</svelte:head>

<button onclick={toggle}>
toggle
</button>
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