fix: memoize per-drag derived values to keep drag.dragover cheap#2555
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christianhg wants to merge 1 commit into
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fix: memoize per-drag derived values to keep drag.dragover cheap#2555christianhg wants to merge 1 commit into
drag.dragover cheap#2555christianhg wants to merge 1 commit into
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The drop-indicator and `deserialization.success` guards both compute `getDragSelection`, `getSelectedBlocks`, and `isSelectingEntireBlocks` on every `drag.dragover` event. These derive from `dragOrigin.selection` which is stable for the entire drag, but the recomputation is O(N) over the dragged range every event. A single drag with "select all" on a 1000-block document was spending ~10ms per dragover (~600+ events per drag). Memoize the derived values on a `WeakMap` keyed on `dragOrigin`. The first event populates the cache, subsequent events do an O(1) lookup. `getFocusBlock` for the drop position is the only per-event tree walk.
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📦 Bundle Stats —
|
| Metric | Value | vs main (c2ec808) |
|---|---|---|
| Internal (raw) | 733.2 KB | -144 B, -0.0% |
| Internal (gzip) | 140.0 KB | +67 B, +0.0% |
| Bundled (raw) | 1.33 MB | -147 B, -0.0% |
| Bundled (gzip) | 300.2 KB | +63 B, +0.0% |
| Import time | 94ms | -0ms, -0.4% |
@portabletext/editor/behaviors
| Metric | Value | vs main (c2ec808) |
|---|---|---|
| Internal (raw) | 467 B | - |
| Internal (gzip) | 207 B | - |
| Bundled (raw) | 424 B | - |
| Bundled (gzip) | 171 B | - |
| Import time | 2ms | -0ms, -0.4% |
@portabletext/editor/plugins
| Metric | Value | vs main (c2ec808) |
|---|---|---|
| Internal (raw) | 3.1 KB | - |
| Internal (gzip) | 967 B | - |
| Bundled (raw) | 2.9 KB | - |
| Bundled (gzip) | 899 B | - |
| Import time | 8ms | -0ms, -1.0% |
@portabletext/editor/selectors
| Metric | Value | vs main (c2ec808) |
|---|---|---|
| Internal (raw) | 76.5 KB | - |
| Internal (gzip) | 13.7 KB | - |
| Bundled (raw) | 71.9 KB | - |
| Bundled (gzip) | 12.6 KB | - |
| Import time | 7ms | -0ms, -0.6% |
@portabletext/editor/utils
| Metric | Value | vs main (c2ec808) |
|---|---|---|
| Internal (raw) | 27.8 KB | - |
| Internal (gzip) | 5.5 KB | - |
| Bundled (raw) | 25.4 KB | - |
| Bundled (gzip) | 5.1 KB | - |
| Import time | 6ms | -0ms, -0.3% |
🗺️ . · ./behaviors · ./plugins · ./selectors · ./utils · Artifacts
Details
- Import time regressions over 10% are flagged with
⚠️ - Sizes shown as raw / gzip 🗜️. Internal bytes = own code only. Total bytes = with all dependencies. Import time = Node.js cold-start median.
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The drop-indicator and
deserialization.successguards both computegetDragSelection,getSelectedBlocks, andisSelectingEntireBlockson everydrag.dragoverevent. These derive fromdragOrigin.selectionwhich is stable for the entire drag, but the recomputation is O(N) over the dragged range every event.A single drag with "select all" on a 1000-block document was spending ~10ms per dragover (~600+ events per drag). Most of that cost is in
getSelectedBlockswalking the keyed range andisSelectingEntireBlocksrecomputing block boundaries — none of which can change while the drag is in flight.Memoize the derived values on a
WeakMapkeyed ondragOrigin. The first event populates the cache, subsequent events do an O(1) lookup.getFocusBlockfor the drop position is the only per-event tree walk that's actually necessary.The
dragOriginobject reference is stable for the entire drag (assigned once ininternalDragatdrag.dragstart, returned by reference on everygetSnapshot()call), so the WeakMap entry is reachable until the drag ends andinternalDragis cleared.Behavior is unchanged. Cross-browser dnd tests green on chromium, firefox, and webkit.
Measurements
1000-block document, 100 dragover events per scenario:
The remaining cost per dragover is
getFocusBlockfor the drop position which depends on the drop position changing every event.