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fix(web): ensure x-list scrolltolower observer sentinel is detectable #2484

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Merged
Sherry-hue merged 1 commit into from
Apr 22, 2026
Merged

fix(web): ensure x-list scrolltolower observer sentinel is detectable #2484

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7 changes: 7 additions & 0 deletions .changeset/wild-wolves-love.md
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Original file line number Diff line number Diff line change
@@ -0,0 +1,7 @@
---
"@lynx-js/web-elements": patch
---

fix: list `bindscrolltolower` may not trigger because the lower threshold
sentinel had no effective size or offset, causing the bottom
`IntersectionObserver` to miss the list boundary
2 changes: 2 additions & 0 deletions packages/web-platform/web-core-e2e/server-tests/__snapshots__/server-e2e.test.ts.snap
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Expand Up @@ -73,6 +73,7 @@ exports[`executeTemplate should run lepusCode.root from basic-element-list-basic
<div
class="observer placeholder-dom"
id="upper-threshold-observer"
part="upper-threshold-sentinel"
></div>
</div>
<slot part="slot"></slot>
Expand All @@ -83,6 +84,7 @@ exports[`executeTemplate should run lepusCode.root from basic-element-list-basic
<div
class="observer placeholder-dom"
id="lower-threshold-observer"
part="lower-threshold-sentinel"
></div>
</div></div></template></x-list
></x-view></div></template
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31 changes: 31 additions & 0 deletions packages/web-platform/web-elements/src/elements/XList/x-list.css
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Expand Up @@ -157,6 +157,37 @@ x-list[x-enable-scrolltoloweredge-event]::part(lower-threshold-observer) {
display: flex;
}

x-list[x-enable-scrolltoupper-event]::part(upper-threshold-sentinel),
x-list[x-enable-scrolltoupperedge-event]::part(upper-threshold-sentinel),
x-list[x-enable-scrolltolower-event]::part(lower-threshold-sentinel),
x-list[x-enable-scrolltoloweredge-event]::part(lower-threshold-sentinel) {
flex: 0 0 1px;
}

x-list[x-enable-scrolltoupper-event]::part(upper-threshold-sentinel),
x-list[x-enable-scrolltoupperedge-event]::part(upper-threshold-sentinel) {
margin-bottom: -1px;
}

x-list[x-enable-scrolltolower-event]::part(lower-threshold-sentinel),
x-list[x-enable-scrolltoloweredge-event]::part(lower-threshold-sentinel) {
margin-top: -1px;
transform: translateY(1px);
}

x-list[scroll-orientation="horizontal"][x-enable-scrolltoupper-event]::part(upper-threshold-sentinel),
x-list[scroll-orientation="horizontal"][x-enable-scrolltoupperedge-event]::part(upper-threshold-sentinel) {
margin-bottom: 0;
margin-right: -1px;
}

x-list[scroll-orientation="horizontal"][x-enable-scrolltolower-event]::part(lower-threshold-sentinel),
x-list[scroll-orientation="horizontal"][x-enable-scrolltoloweredge-event]::part(lower-threshold-sentinel) {
margin-top: 0;
margin-left: -1px;
transform: translateX(1px);
}

x-list::part(lower-threshold-observer) {
flex-direction: column-reverse;
}
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2 changes: 2 additions & 0 deletions packages/web-platform/web-elements/src/elements/htmlTemplates.ts
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Expand Up @@ -148,6 +148,7 @@ export const templateXList = `<style>
<div
class="observer placeholder-dom"
id="upper-threshold-observer"
part="upper-threshold-sentinel"
></div>
</div>
<slot part="slot"></slot>
Expand All @@ -158,6 +159,7 @@ export const templateXList = `<style>
<div
class="observer placeholder-dom"
id="lower-threshold-observer"
part="lower-threshold-sentinel"
></div>
</div>
</div>`;
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2 changes: 2 additions & 0 deletions packages/web-platform/web-elements/src/template.rs
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Expand Up @@ -155,6 +155,7 @@ pub const TEMPLATE_X_LIST: &str = r#"<style>
<div
class="observer placeholder-dom"
id="upper-threshold-observer"
part="upper-threshold-sentinel"
></div>
</div>
<slot part="slot"></slot>
Expand All @@ -165,6 +166,7 @@ pub const TEMPLATE_X_LIST: &str = r#"<style>
<div
class="observer placeholder-dom"
id="lower-threshold-observer"
part="lower-threshold-sentinel"
></div>
</div>
</div>"#;
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