Feat: Add scope to event handlers

[jlukic]

Event handlers' data now includes the template vars at the event target — each item vars, subtemplate args, snippet args, async values:

'click .destroy'({ self, data }) {
  self.deleteTodo(data.id);
}

Removes the data-id round trip for list handlers. Template vars merge below data attributes and event.detail, so existing handlers keep their values.

Additional Changes

• list-event-data docs example
• todo-list drops its data-id attributes
• +1.5KB min / +0.4KB brotli

Risk

5/10

The data argument every event handler receives now merges template vars below its existing sources — all event handling flows through changed code.

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Project	Deployment	Actions	Updated (UTC)
semantic-next	Ready	Preview, Comment	Jun 11, 2026 10:13pm

1 Skipped Deployment

Project	Deployment	Actions	Updated (UTC)
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[semantic-performance-bot]

⚪ No Meaningful Change for 9e54588 on Benchmark Suite 📊

Base: main · Action: #27380684456 · Raw: bench-report.json

^{Feat: Add scope to event handlers}

Note

This PR did not move any measured metrics.

✅ 0 faster · ❌ 0 slower · 🔍 28 unsure · ⚪ 21 no change · 📜 1 reopened

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📜 Regressions from peak (1)

These metrics were faster on an earlier push to this PR. The most recent candidate is usually where to look.

metric	regression	prior peak	likely candidates
krausest:replace-1k	3%	e0b4a20	60f4a5e

⚪ No Change (21)

Metrics where this PR measured within ±2% of main — no meaningful performance change detected.

metric	Change
build-html-string-10k	-1.1% – +0.6%
todo:bulk-add-500	+0.0% – +1.1%
krausest:clear-10k	+0.3% – +1.9%
todo:clear-completed-250	-0.8% – +1.0%
krausest:create-10k	-0.0% – +0.8%
dom-walker-1000x15	-1.0% – +1.3%
each-100	-0.5% – +1.0%
each-100-mount	-0.8% – +1.0%
template:each-mount-1000	-1.9% – -0.6%
todo:edit-start-10	-0.9% – +0.8%
expr-lisp-50k	-1.5% – +1.2%
todo:filter-cycle-20	+0.1% – +1.4%
helper-100-mount	-1.2% – +0.7%
todo:remove-50-front	-1.9% – +1.9%
template:snippet-args-per-key-100x500	-0.7% – +1.2%
template:subtemplate-data-blob-100	-0.1% – +1.7%
template:subtemplate-helpers-heavy-100x500	-1.6% – +1.1%
template:subtemplate-helpers-light-100x500	-1.4% – +1.4%
template:subtemplate-reactive-data-100x500	-0.6% – +1.3%
template:subtemplate-shorthand-props-100x500	-1.4% – +1.4%
todo:toggle-all-200	+0.5% – +1.1%

🔍 Unsure (28)

Too Fast to Measure Precisely (28)

On benches this short, OS jitter, GC, and JIT pauses drown out anything under 4%. Bigger changes than that still show up.

metric	Change	Test Time	Expected Noise
template:active-indicator-200	-2.5% – +1.0%	~34ms	±6%
template:active-indicator-nested-200	-2.1% – +4.7%	~21ms	±11%
todo:add-20	-2.1% – +1.3%	~11ms	±2%
krausest:append-1k	-2.5% – +2.9%	~53ms	±7%
krausest:create-1k	-3.5% – +0.4%	~46ms	±3%
todo:edit-cycle-5	-2.3% – +1.1%	~65ms	±4%
expr-js-10k	-0.4% – +2.2%	~19ms	±6%
expr-simple-100k	-1.1% – +2.4%	~22ms	±8%
helper-100-state-change-1k	-0.7% – +2.3%	~4ms	±7%
todo:remove-50-back	+0.4% – +2.3%	~5ms	±2%
todo:remove-50-middle	-4.0% – +2.7%	~7ms	±9%
todo:remove-first-100	-0.8% – +4.2%	~14ms	±6%
todo:remove-last-100	-0.8% – +2.4%	~14ms	±3%
todo:remove-middle-100	-0.2% – +9.2%	~13ms	±12%
krausest:remove-row-back-100	-0.7% – +4.7%	~15ms	±7%
krausest:remove-row-front-20	-3.5% – +2.6%	~5ms	±9%
krausest:remove-row-middle-20	-2.6% – +5.5%	~3ms	±6%
todo:rename-500	-5.5% – +4.6%	~18ms	±12%
krausest:replace-1k	+0.2% – +2.7%	~59ms	±3%
krausest:select-40	-3.1% – +3.3%	~3ms	±9%
template:snippet-in-subtemplate-100x1k	-2.1% – +1.6%	~21ms	±6%
template:stable-ref-mutate-500	-3.6% – +1.5%	~14ms	±9%
krausest:swap-rows-20	-3.0% – +2.6%	~7ms	±4%
todo:toggle-100	-0.1% – +7.8%	~13ms	±10%
todo:toggle-first-100	-2.3% – +3.2%	~15ms	±7%
todo:toggle-last-100	-1.2% – +3.5%	~15ms	±6%
todo:toggle-middle-100	-1.5% – +3.6%	~13ms	±8%
krausest:update-10th-50	-0.7% – +3.1%	~15ms	±5%

📖 Bench glossary (40 metrics)

metric	what it tests
krausest:append-1k	Appends 1000 new rows onto an existing 1000-row table.
krausest:clear-10k	Clears a 10000-row table back to empty in a single operation.
krausest:create-10k	Renders a fresh 10000-row table into an empty parent at ten times the create-1k scale.
krausest:create-1k	Renders a fresh 1000-row table into an empty parent.
krausest:remove-row-back-100	Removes the last row 100 times from a 1000-row table, with no other rows needing to move.
krausest:remove-row-front-20	Removes the first row 20 times from a 1000-row table, with all remaining rows sliding up each time.
krausest:remove-row-middle-20	Removes the middle row 20 times from a 1000-row table, with the rows below it sliding up each time.
krausest:replace-1k	Replaces 1000 rows with a fresh 1000-row set, diffing the keyed list against a populated table.
krausest:select-40	Highlights one row at a time across 40 rows so only the previous and newly highlighted rows update.
krausest:swap-rows-20	Swaps the second and second-to-last rows in a 1000-row table, repeated 20 times.
krausest:update-10th-50	Updates the label on every tenth row of a 1000-row table, looped 50 times to lift the work above noise.
template:active-indicator-200	Cycles selectedId across 200 list items. Only the previously and newly active items update their class.
template:active-indicator-nested-200	Cycles currentUrl through 50 leaf urls in a 5×10×4 nav. Only the previously and newly active leaves should update their…
template:each-mount-1000	Mounts a fresh 1000-item each block with five-field items so per-record allocation cost dominates the wall clock.
template:snippet-args-per-key-100x500	Mutates one snippet arg's source across 100 invocations, 500 cycles. Adjacent no-signal expressions stay quiet.
template:snippet-in-subtemplate-100x1k	Mutates one subtemplate prop's source across 25 cards each invoking 4 inner snippets, 1000 cycles. Snippet bodies shoul…
template:stable-ref-mutate-500	Replaces one item by index in a 500-item list across 100 cycles. Only that item's expressions re-render.
template:subtemplate-data-blob-100	Mutates one field inside data=expression on 100 children. Every child re-renders by design.
template:subtemplate-helpers-heavy-100x500	100 subtemplates, 4 inner bindings where three call helpers shaped like userland reality — Intl.NumberFormat, Array.fin…
template:subtemplate-helpers-light-100x500	100 subtemplates, 4 inner bindings each calling formatDate / classIf / capitalize, 500 cycles. Mutates one source signa…
template:subtemplate-reactive-data-100x500	Mutates one verbose reactiveData field across 100 child subtemplates, 500 cycles. Only the changed field re-evaluates.
template:subtemplate-shorthand-props-100x500	Mutates one shorthand prop's source across 100 child subtemplates, 500 cycles. Only that prop re-evaluates.
todo:add-20	Appends 20 todo items one at a time, like a user typing entries in a row.
todo:bulk-add-500	Renders 500 todo items added at once from a single data load.
todo:clear-completed-250	Clears 250 completed items from a 500-item list in one action, like clicking clear completed.
todo:edit-cycle-5	Runs 5 full edit-then-save cycles on different items, like editing a row and saving it.
todo:edit-start-10	Enters edit mode on 10 different items in a row, like double-clicking each one.
todo:filter-cycle-20	Cycles through active, completed, and all filters 20 times on a 100-item list.
todo:remove-50-back	Deletes 50 items from the end of a 100-item list, one click at a time.
todo:remove-50-front	Deletes 50 items from the front of a 100-item list, one click at a time.
todo:remove-50-middle	Deletes 50 items from the middle of a 100-item list, one click at a time.
todo:remove-first-100	Deletes the first item 100 times from a 200-item list, with remaining items moving up each time.
todo:remove-last-100	Deletes the last item 100 times from a 200-item list, with no other items needing to move.
todo:remove-middle-100	Deletes the middle item 100 times from a 200-item list, walking halfway through to find each target.
todo:rename-500	Renames items in a 100-item list 500 times via single-field setProperty without editingId co-fires.
todo:toggle-100	Cycles through the first 10 items 10 times each, like a user toggling items repeatedly down a list.
todo:toggle-all-200	Toggles all 100 items completed and back across 200 cycles via the master checkbox.
todo:toggle-first-100	Toggles the first item in a 100-item list 100 times, alternating completed on and off.
todo:toggle-last-100	Toggles the last item in a 100-item list 100 times, alternating completed on and off.
todo:toggle-middle-100	Toggles a middle item in a 100-item list 100 times, alternating completed on and off.

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_{Sample size: 80 floor / 280 max · Noise floor: ±2% · Timeout: 3min · Wall-clock: 12m03s}