[labs/observers] Allow ResizeController to observe individual elements in Lit templates #5111

justinfagnani · 2025-10-02T01:19:41Z

Fixes #5110

This adds a .target() method to ResizeController that returns a directive that observes that element specifically.

…s in Lit templates

changeset-bot · 2025-10-02T01:19:44Z

🦋 Changeset detected

Latest commit: bbf1971

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@lit-labs/observers	Minor

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github-actions · 2025-10-02T01:19:52Z

📊 Tachometer Benchmark Results

Summary

nop-update

this-change, tip-of-tree, previous-release: faster ✔ 1% - 14% (0.05ms - 1.77ms)
^{this-change vs tip-of-tree}

render

this-change: 45.19ms - 59.40ms
this-change, tip-of-tree, previous-release: unsure 🔍 -6% - +6% (-1.27ms - +1.14ms)
^{this-change vs tip-of-tree}
this-change, tip-of-tree, previous-release: unsure 🔍 -3% - +1% (-1.22ms - +0.22ms)
^{this-change vs tip-of-tree}
this-change, tip-of-tree, previous-release: unsure 🔍 -39% - +3% (-24.98ms - +3.44ms)
^{this-change vs tip-of-tree}

update

this-change: 483.05ms - 495.47ms
this-change, tip-of-tree, previous-release: unsure 🔍 -1% - +10% (-0.15ms - +3.69ms)
^{this-change vs tip-of-tree}
this-change, tip-of-tree, previous-release: unsure 🔍 -4% - +0% (-3.38ms - +0.10ms)
^{this-change vs tip-of-tree}
this-change, tip-of-tree, previous-release: unsure 🔍 -0% - +2% (-2.26ms - +9.53ms)
^{this-change vs tip-of-tree}

update-reflect

this-change: 466.02ms - 475.87ms
this-change, tip-of-tree, previous-release: unsure 🔍 -1% - +1% (-4.36ms - +5.82ms)
^{this-change vs tip-of-tree}

Results

this-change

Browser: chrome-headless 140.0.0.0
Sample size: 50
Built by: Benchmarks #6991
Commit: bbf1971

render

Version	Avg time	vs
	45.19ms - 59.40ms	-

update

Version	Avg time	vs
	483.05ms - 495.47ms	-

update-reflect

Version	Avg time	vs
	466.02ms - 475.87ms	-

this-change, tip-of-tree, previous-release

Browser: chrome-headless 140.0.0.0
Sample size: 30
Built by: Benchmarks #6991
Commit: bbf1971

render

Version	Avg time	vs this-change	vs tip-of-tree tip-of-tree	vs previous-release previous-release
this-change	19.61ms - 21.23ms	-	unsure 🔍 -6% - +6% -1.27ms - +1.14ms	unsure 🔍 -4% - +6% -0.81ms - +1.27ms
tip-of-tree tip-of-tree	19.59ms - 21.38ms	unsure 🔍 -6% - +6% -1.14ms - +1.27ms	-	unsure 🔍 -4% - +7% -0.81ms - +1.41ms
previous-release previous-release	19.53ms - 20.84ms	unsure 🔍 -6% - +4% -1.27ms - +0.81ms	unsure 🔍 -7% - +4% -1.41ms - +0.81ms	-

update

Version	Avg time	vs this-change	vs tip-of-tree tip-of-tree	vs previous-release previous-release
this-change	37.41ms - 40.09ms	-	unsure 🔍 -1% - +10% -0.15ms - +3.69ms	unsure 🔍 -2% - +7% -0.73ms - +2.66ms
tip-of-tree tip-of-tree	35.60ms - 38.35ms	unsure 🔍 -9% - +0% -3.69ms - +0.15ms	-	unsure 🔍 -7% - +2% -2.53ms - +0.92ms
previous-release previous-release	36.74ms - 38.82ms	unsure 🔍 -7% - +2% -2.66ms - +0.73ms	unsure 🔍 -3% - +7% -0.92ms - +2.53ms	-

nop-update

Version	Avg time	vs this-change	vs tip-of-tree tip-of-tree	vs previous-release previous-release
this-change	11.31ms - 12.32ms	-	faster ✔ 1% - 14% 0.05ms - 1.77ms	faster ✔ 1% - 13% 0.04ms - 1.68ms
tip-of-tree tip-of-tree	12.03ms - 13.43ms	slower ❌ 0% - 15% 0.05ms - 1.77ms	-	unsure 🔍 -7% - +8% -0.89ms - +1.00ms
previous-release previous-release	12.04ms - 13.32ms	slower ❌ 0% - 14% 0.04ms - 1.68ms	unsure 🔍 -8% - +7% -1.00ms - +0.89ms	-

this-change, tip-of-tree, previous-release

Browser: chrome-headless 140.0.0.0
Sample size: 50
Built by: Benchmarks #6991
Commit: bbf1971

render

Version	Avg time	vs this-change	vs tip-of-tree tip-of-tree	vs previous-release previous-release
this-change	35.20ms - 36.08ms	-	unsure 🔍 -3% - +1% -1.22ms - +0.22ms	unsure 🔍 -2% - +1% -0.81ms - +0.47ms
tip-of-tree tip-of-tree	35.56ms - 36.70ms	unsure 🔍 -1% - +3% -0.22ms - +1.22ms	-	unsure 🔍 -1% - +3% -0.41ms - +1.06ms
previous-release previous-release	35.35ms - 36.27ms	unsure 🔍 -1% - +2% -0.47ms - +0.81ms	unsure 🔍 -3% - +1% -1.06ms - +0.41ms	-

update

Version	Avg time	vs this-change	vs tip-of-tree tip-of-tree	vs previous-release previous-release
this-change	72.00ms - 74.36ms	-	unsure 🔍 -4% - +0% -3.38ms - +0.10ms	unsure 🔍 -3% - +2% -2.46ms - +1.40ms
tip-of-tree tip-of-tree	73.54ms - 76.10ms	unsure 🔍 -0% - +5% -0.10ms - +3.38ms	-	unsure 🔍 -1% - +4% -0.89ms - +3.10ms
previous-release previous-release	72.18ms - 75.24ms	unsure 🔍 -2% - +3% -1.40ms - +2.46ms	unsure 🔍 -4% - +1% -3.10ms - +0.89ms	-

this-change, tip-of-tree, previous-release

Browser: chrome-headless 140.0.0.0
Sample size: 50
Built by: Benchmarks #6991
Commit: bbf1971

render

Version	Avg time	vs this-change	vs tip-of-tree tip-of-tree	vs previous-release previous-release
this-change	40.76ms - 59.80ms	-	unsure 🔍 -39% - +3% -24.98ms - +3.44ms	unsure 🔍 -33% - +15% -18.92ms - +8.98ms
tip-of-tree tip-of-tree	50.50ms - 71.59ms	unsure 🔍 -10% - +53% -3.44ms - +24.98ms	-	unsure 🔍 -17% - +38% -8.86ms - +20.47ms
previous-release previous-release	45.05ms - 65.44ms	unsure 🔍 -19% - +39% -8.98ms - +18.92ms	unsure 🔍 -32% - +13% -20.47ms - +8.86ms	-

update

Version	Avg time	vs this-change	vs tip-of-tree tip-of-tree	vs previous-release previous-release
this-change	484.14ms - 491.87ms	-	unsure 🔍 -0% - +2% -2.26ms - +9.53ms	unsure 🔍 -1% - +1% -6.54ms - +5.66ms
tip-of-tree tip-of-tree	479.92ms - 488.83ms	unsure 🔍 -2% - +0% -9.53ms - +2.26ms	-	unsure 🔍 -2% - +0% -10.56ms - +2.42ms
previous-release previous-release	483.72ms - 493.17ms	unsure 🔍 -1% - +1% -5.66ms - +6.54ms	unsure 🔍 -1% - +2% -2.42ms - +10.56ms	-

update-reflect

Version	Avg time	vs this-change	vs tip-of-tree tip-of-tree	vs previous-release previous-release
this-change	488.53ms - 495.98ms	-	unsure 🔍 -1% - +1% -4.36ms - +5.82ms	unsure 🔍 -1% - +1% -3.19ms - +7.26ms
tip-of-tree tip-of-tree	488.06ms - 494.99ms	unsure 🔍 -1% - +1% -5.82ms - +4.36ms	-	unsure 🔍 -1% - +1% -3.73ms - +6.35ms
previous-release previous-release	486.55ms - 493.88ms	unsure 🔍 -1% - +1% -7.26ms - +3.19ms	unsure 🔍 -1% - +1% -6.35ms - +3.73ms	-

_{tachometer-reporter-action v2 for Benchmarks}

github-actions · 2025-10-02T01:21:31Z

The size of lit-html.js and lit-core.min.js are as expected.

[labs/observers] Allow ResizeController to observe individual element…

bbf1971

…s in Lit templates

justinfagnani requested a review from sorvell October 2, 2025 01:19

justinfagnani requested a review from kevinpschaaf as a code owner October 2, 2025 01:19

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[labs/observers] Allow ResizeController to observe individual elements in Lit templates #5111

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📊 Tachometer Benchmark Results

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update

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📊 Tachometer Benchmark Results

Summary

nop-update

render

update

update-reflect

Results

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update

update-reflect

render

update

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render

update

update-reflect

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